CONTENTS
PAGS
INTRODUCTION
Methods and cooperation
Additional control areas needed
IDENTIFICATION
421
_ ' 473
475
ZIIIIZII'IZZZZI 475
Descriptions
"
* 475
Measurements and weights
477
The antelope jack rabbit (Lepus alleni)
Z Z Z Z Z Z 477
The Arizona jack rabbit (Lepus califomicus eremicus)
478
Structural adaptations in the jack rabbits
478
DISTRIBUTION AND HABITAT
*„". Z Z Z Z Z 478
Lepus alleni
478
The Lepus califomicus group
" *" 481
GENERAL HABITS
1..L. 482
Gregariousness
482
Daily movements
483
Seasonal migrations
484
Extent of home range...
485
Attitudes and movements
486
The rump-flash
488
Running, jumping, and swimming
489
Senses
490
BREEDING HABITS
491
Life span
492
Sex ratio
492
Breeding season and rate
493
Sex behavior
499
Voice
499
Fighting
499
Physical characteristics in the breeding season
501
Forms, nests, and young
501
Forms
502
Nests
504
Habits and development of young
506
FOOD
510
Rabbits and vegetation
„
* 510
Quantity of food eaten
514
Feeding tests and computations
514
Correction in equivalents
- 516
Forage consumption by rodents
516
Food of jack rabbits as shown by stomach analyses
519
Lepus alleni
522
Lepus californicus
524
Jack rabbits and browse
526
Mesquite
526
Other species
528
Jack rabbits and cactus
529
Distribution of cactus
533
Drouth and over-grazing critical
534
Spines as a protection to desert plants
535
Jack rabbits and grass
- 535
Lepus alleni.
535
Lepus californicus..,.
,
*
536
General effects
536
Jack rabbits and weeds
539
Jack rabbits and crops
•
541
Animal food
§2*
Mineral elements
•
£J*
m
Feeding
---
PAGfi
ENEMIES
Coyote
General relations
Rabbits in coyote stomachs
Seasonal, cyclical, and local aspects
Check and balance relations
Bobcat
Snakes
Birds
Miscellaneous
Concluding remarks on enemies
PARASITES AND DISEASES
Arthropods
Tapeworms and nernatodes
Tularemia and other diseases
NUMBERS
Fluctuations
Jack rabbit counts
Pellet counts
Grass and jack rabbit abundance
Estimated weight of jack rabbits on the range
ECONOMIC STATUS
Crop damage
Range damage
Forest damage
Value of jack rabbits
The jack rabbit a safety factor
CONTRpL
Rabbits in Australia
Biological control
The balance of nature
Direct methods
A fundamental principle
SUMMARY
BIBLIOGRAPHY
543
543
543
544
545
545
546
546
547
548
548
549
549
551
554
555
555
556
559
563
564
564
564
565
566
566
567
569
569
571
575
576
578
579
583
ILLUSTRATIONS
PAGE
Fig. 1.—Range, in Arizona, of Lepus alleni compared with that of Lepus californicus ssp. Lepus californicus occurs all over the state
Fig. 2.—Percentage consumption of food of L. alleni throughout the year
Fig. 3.—Percentage consumption of food of L. californicus eremkus throughout the year
Fig. 4.—Dotted lines show routes traversed in making jack rabbit-cow counts..
Fig. 5.—Diagram of bio-physical complex
479
524
525
558
574
PLATES
Plate 1
Frontispiece
Plate 2
487
Plate 3
503
Plate 4
507
Plate
5
517
Plate 6.
520
Plate 7
521
Plate 8
530
Plate 9
532
Plate 10
Plate 11
Plate 12
-
540
552
562
THE LIFE HISTORIES AND ECOLOGY OF
JACK RABBITS,
LBPUS ALLBNI AND LUPUS CAUPORNICUS SSP.3
IN RELATION TO GRAZING IN ARIZONA
BY
T. VORHICS, Entomologist,
Agricultural Experiment Station,
University of Arizona,
CHARTS
AND
P. TAYLOR, Senior Biologist,
United States Department of Agriculture,
Bureau of Biological Survey.
WAIVT^R
INTRODUCTION
The jack rabbit, m its proper place, is a picturesque and to some
extent a useful citizen. But what, under modern conditions, is its
proper place ? Not, to be sure, on the alfalfa fields or other crop lands
in farming districts. Certainly not in foreign countries or in lands far
from its natural area of distribution. Stories of bringing the rabbit
of Europe into England and the same species into Australia and New
Zealand are fraught with interest and full of significance. They carry
an unmistakable warning to the "introductionists." A critical scientist
f Farrow, 1925, p. 104) has gone so far as to suggest that "The passing
of England from a forest period into a grassland period may of late
have been accelerated by the influence of rabbits." The situation in
Australia is still more serious According to Stead (1928, p. 5), "Probably it will be agreed that no single circumstance in the history of Australia has so profoundly affected the economic development of our pastoral and agricultural industries as the introduction of the European
wild rabbit." These are strong words. Let us translate them into
concretes. The lowly rabbit, a more profound influence on the economic development of the country, at least during the period referred
to by Stead, than problems of capital and labor, tariff, immigration,
interracial and international relations! The further one goes, however,
in the study of conditions on that continent, the more readily he comes
to agree that Stead's comment is by no means overdrawn.
Nor do we have to go to foreign countries for illustrations of potential damage by jack rabbits. In the valleys of California, and in the
arid lands of the intermountain region, as eastern Oregon, eastern
Washington, Wyoming, Colorado, Idaho, Utah, and Nevada, jack rabbits have not infrequently attained to plague status, warranting, yes,
necessitating, drastic control measures as a price of crop security.
472
TBCHXICAL BULLETIN
Ko. 49
The story is not all unfavorable, however, to our long-eared cornpadre. Some people use its ample carcass for food, and there is no
reason why, with proper precautions, this use should not be extended.
The jack rabbit is a "key-industry" species, affording sustenance to a
variety of flesh-eating mammals, which otherwise might give more attention to poultry, lambs, calves, quail, and other game birds, in the
conservation of which man has a decided interest.
We must apparently surrender the cherished idea that wild creatures
generally, and in their native habitats, are either wholly good or wholly
bad. A broad and open-minded view should be taken toward the lesser inhabitants of our globe. Such an attitude is only fair to our
animal colleagues, and more than this, it is the only safe course for
ourselves. History shows that mankind has frequently been guilty of
policies and practices in reference to natural resources that have resulted
in inexcusable waste and have made man himself poorer. At intervals
all our policies for the regulation of natural resources should be given
a critical re-examination in the light of the latest information. Only in
this way can we be reasonably sure we are giving present and future
generations a square deal.
As our knowledge of wild life problems increases, we are compelled
to conclude that: (1) problems involving particular animals and plants
are different in different places, and should be worked out with full
knowledge of local conditions; (2) problems involving particular animals or plants can be solved only when attention is given to the interrelationships existing between the species involved and all other important species. Interrelationships with environment also are of vital
importance.
Studies in biology, as with this study of the jack rabbit, can never
be up-to-date. Nature's great equation is always changing. Factors
are dropped out here and there; others are introduced. It is obvious
that many human enterprises affect jack rabbit status — among them:
(1) bringing new lands under irrigation; (2) grazing by livestock;
(3) predatory animal and rodent control; (4) deforestation. The research job, in biology, is never done. Published books and papers are
at best but progress reports. These facts do not detract from, but
rather add to, the need for research and the publication of research.
We would like to be able to answer all the questions that have arisen,
and to present, in simple words and clear, formulas for regulating the
jack rabbit under all conditions to man's advantage. Unfortunately,
*ucb deiiniteness of statement is impracticable. It is disappointing perhaps, that we have been able merely to open the subject rather than to
settle all the problems that have arisen in connection with it. Recall,
however, that studies in the wild life field, though now given much less
JACK RABBITS IN ARIZ OXA
473
financial support, are infinitely more difficult than those, say, in physics
and chemistry. "The motions of the solar system since its beginning
are less complicated than the play of a child for a day" (Cattell, 1929,
p. 336). It should be remembered, too, that in the long run, biological
studies, since they deal with living matter, behavior, population, food,
shelter, adaptation, environment, and heredity, promise more, perhaps,
for the future welfare of mankind than all other investigations put
together. W e humans are animals, dependent for our living on other
animals and on plants. Studies of individual and community relationships involved in the world of living things should be the most useful
as well as the most fascinating pursuit open to mankind.
Field work for the present study of the jack rabbit was done almost
exclusively in southern Arizona. Specific conclusions reached apply
only in that or closely similar regions. Free use has been made, however, of available pertinent information that seems to throw any light
on the questions that arose during the course of the study.
M E T H O D S AND C O O P E R A T I O N
During the period of his residence in Tucson, Vorhies (since 1915)
has taken an interest in the jack rabbits of the vicinity and at intervals
has given time to their study in the field. Beginning" during short visits
in 1918, and continuing during a period of residence beginning in 1922,
Taylor has likewise been concerned at intervals with the ecology of
the jack rabbit. Field work by the writers has been done both separately and together. Most of the actual investigations have been conducted on the Santa Rita Experimental Range, but personal field work
has been done west through California (Vorhies and Taylor), north to
central Utah (Taylor), east through Texas (Taylor), and south to
Libertad, Hermosillo, and Kino Bay, Sonora, Mexico (Vorhies),
The Santa Rita Experimental Range is a tract of nearly 50,000 acres
located at the northwest base of the Santa Rita Mountains about 35
miles south of Tucson, Arizona. It lies on a bahada* between altitudes
of 2,700 and 4,500 feet, and includes a variety of types of vegetation of
the semi-arid country.
The Jornada Experimental Range is a similar, but larger, grazing
range experiment station near Las Cruces, New Mexico. Both these
areas are under the administrative control of the United States Forest
Service.
*A long, gently sloping land form, usually made up of contiguous alluvial fans,
occurring about the bases of some of the southern Arizona mountains. Bahadas
are intermediate between the plains of the valley bottom and foothills. They
are usually well grassed as compared with lower-lying areas.
474
TECHNICAL BULLETIN No. 49
Some years ago (Vorhies and Taylor, 1922, p. 3) the Agricultural
Experiment Station of the University of Arizona, the United States
Biological Survey, the Carnegie Institution of Washington, and the
United States Forest Service undertook a study of the ecology of the
range lands of the Southwest, the work being centered on the Santa
Rita Range, and including investigations of the life histories of rabbits
and the more important rodents and their relations to vegetation. The
present paper is based on this work.
The preparation of this bulletin has been facilitated by a number of
workers. Dr. Frederic E. Clements, of the Carnegie Institution of
Washington, has given active cooperation. Officers of the Southwestern Forest and Range Experiment Station, especially G. A. Pearson,
director, C. K. Cooperrider, senior range examiner in charge of
grazing investigations, and P. B. Lister and Matt Culley (director) of
the Santa Rita Experimental Range, have extended us numerous courtesies, as did also R. L. Hensel and R. R. Hill, former directors. The
stockmen who run their cattle on the Santa Rita Range have been helpful in many ways. Special mention, in this connection, should be made
of cooperation by Mr. W. D. Parker. Professor McGinnies, of the
Department of Range Ecology of the University of Arizona, participated in some of the field work (charting quadrats, and taking vegetative notes).
M. E. Mttsgrave (Forest Service), and D. A. Gilchrist, regional supervisor, rodent and predatory animal control, southwestern district, (Biological Survey*) have been helpful. A considerable amount of information gathered in New Mexico and Texas has been furnished us by
Don A. Spencer of Control-Methods Research, and Shaler E.
E. Aldous of the Food Habits Research Laboratory, Biological
Survey, Denver, Colorado. Ben E. Foster, leader rodent and
predatory animal control. State of Arizona, and Chas. E. Gillharn, assistant leader, have cooperated in numerous ways. A number
of other Biological Survey workers have furnished important information, among them being: E. E. Horn, John W. Meyer, Joseph Keyes,
P. E. Garlough, Leo L. Laythe, James Silver, Thomas B. Murray, Wallace W. Smith, Otto E. Stephl E. R. Sans, A. E. Gray, John C. Gatlin, Ira N. Gabrielson, Stanley G. Jewett, Laurence C. Whitehead, Cedric R. Landon, George H. Holman, Reuben S. Zimmerman, Leo K.
Couch, Theo. H. Scheffer, and O. J. Mttrie.
C C. Sperry of Food Habits Research, Biological Survey, Washington, D. C, under the direction of W. L. McAtee, in charge, did all the
painstaking work of analysis of the contents of jack rabbit stomachs.
We have had the active cooperation of the authorities of the University of Arizona, especially President H. L. Shantz, Dr. P. S. Burgess,
JACK RABBITS IN ARIZONA
475
dean and director, College of Agriculture; Dr. E. D. Ball, former
dean, College of Agriculture; and A. A. Nichol and D. M. Gorsuch.
Likewise, we have received the most cordial backing and encouragement of Dr. W. B. Bell, principal biologist in charge of the Division of
Biological Investigations, Biological Survey, Washington, D. C, Edward A. Preble, assistant in charge, Stanley P. Young, principal biologist in charge of the Division of Predatory Animal and Rodent Control, and of Paul G. Redington, chief of the bureau.
ADDITIONAL CONTROL AREAS NEEDED
In attempting to determine the role of the jack rabbits on the range
we have been impressed with the need, in all such studies, of more
adequate control areas. We feel that in any bio-ecological problem,
involving the plants, animals, soil, and climate of particular areas, it is
desirable and often essential to have control areas of large size, i.e., several hundred or preferably several thousand acres, under natural conditions, to compare with areas subject to various degrees of modification
by man. Provision, on the Santa Rita Range, of large areas in each
type (semi-desert, mesa, foothill), and embracing*, as far as possible,
every important condition, free from all grazing by cattle, would help
the observer to find the right answers to the questions that are sure
to come up in the course of his work. In the absence of such areas the
answers will lack something in definiteness and collusiveness. Among
the problems to the solution of which large-sized control areas might
be expected to contribute are: life histories, soil relations, and food
habits of native animals (rodents, birds, insects, etc.) ; most productive management of range; range rehabilitation; carrying capacity of
the range for livestock, game and native rodents; game problems; and
erosion on range lands.
IDENTIFICATION
The jack rabbits may be readily distinguished from other rabbits by
their structural characters and habits. Lyon (1904, pp. 386-389) gives
detailed keys to the families, genera, and subgenera of the order Lagomorpha to which all rabbits belong, based on dental, cranial and other
skeletal characters. It is unnecessary to recapitulate these keys, except
to point out that in the skull of the jack rabbits the interparietal is not
present as a distinct bone in adult life, while in the cottontails it is present. In this characteristic the cottontails (genus Sylvilagus) resemble
the European rabbit and the domesticated varieties of rabbits.
In life the jack rabbits can be readily distinguished from the cottontails of the same region by their entirely different habits. While the
476
TECHNICAL BULLETIN No, 49
jack rabbit, on being alarmed, runs with long strides, interrupted by an
occasional observation leap, covering much country in a very short space
of time, the cottontail, under similar conditions, scuttles hurriedly to
cover, humping along* on its relatively short legs, its white tail bobbing
up and down with the motion of its body, the animal dodging artfully
en route to shelter, which is seldom far off. The jack rabbit stops in
the open, poised for another run if necessary. The cottontail generally
disappears in a burrow, although an occasional individual may pause a
moment at the entrance to see what is going to happen next.
The dimensions and weights of the jack rabbits afford a ready means
of separating them from the cottontails.
lepus alleni alleni
Lepus calif arnicas
ercmicus
Svhila^us auduboni
arisonae *
Total
length
622 (670-553)
Tail
vertebrae
58 (76-48)
Hind
foot
140 (150-127)
Ear from
notch
162 (173-133)
556 (630-465)
71 (90-50)
132 (145-112)
139 (163-127)
359
51.4
84.4
68.9
It will be noted that the total length of the cottontail is but 77 percent,
the hind foot 75 percent, and ear from notch 54 percent, of those of the
smallest measured jack rabbit. The weights, too, are distinctive. While
the cottontail weighs but 2-3 pounds, the Arizona jack rabbit weighs
on an average 5.5 pounds, while the antelope jack rabbit tips the scales
at an average of 8 pounds.
The two jack rabbits indigenous to the Tucson region in southern
Arizona (Arizona jack rabbit, Lepus calif onncus eremicus, and antelope
jack rabbit, Lepus alleni alleni) can also be easily distinguished (Plate
1). Their dimensional differences have already been referred to and
are further treated on pages 477, 478. An easy field mark for distinguishing the two at a glance is the color of the tips of their very conspicuous
ears. While the Arizona jack rabbit has the tip of the ear black for
1 to 1 Yz inches, the antelope lacks the black tip.
DESCRIPTIONS
Excellent descriptions of both the Arizona and the antelope jack
rabbits have been published by Nelson (1909, pp. 117-118, 140-141).
These descriptions, supplemented by our own studies of the animals in
the field, and by additional information here given on the weights,
measurements, and structural adaptations of the two species, should suffice to convey at least some notion of their principal characteristics. It
is worthy of remark that Nelson regards Lepus alleni as ". - . the hand* From Nelson, 1909. p. 223.
JACK RABBITS IN ARIZONA
477
somest and most strongly marked of the jack rabbits, its huge ears, long
legs, short tail, and bright color completely differentiating it and making
it one of the most remarkable and striking of American mammals."
MEASUREMENTS AND WEIGHTS
External measurements include: Total length: From tip of nose to
tip of tail vertebrae, measured before skinning. Tail vertebrae: Length
from point in angle when tail is bent at right angles to body to tip
without hairs. Ear from notch: Length from notch at bottom of external opening to tip exclusive of hairs. Hind foot: Length from heel to
tip of longest claw.
It may be noted that alleni is the longest-eared jack rabbit in the
United States, its ears being as much as 8J4 inches in total length measured from head to ear tip. Recorded tail measurements of rabbits are
less satisfactory than in most mammals owing to the difficulty of making
them accurately. They do show, however, that calif ornicus, notwithstanding its smaller size, has a longer tail than alleni. The tail of callfornkus averages 12.7 percent of the total length, while the tail of
alleni averages but 9.4 percent of its total length.
THE ANTELOPE JACK RABBIT (LUPUS AllBNI AILHNI)
Average measurements of S3 adult specimens of both sexes taken
at various localities in Arizona, mostly on the Santa Rita Range: Total
length, 622 millimeters (670-553); tail vertebrae, 58 (76-48) ; ear from
notch, 162 (173-138); hind foot, 140 (150-127). The average weight
of 116 individuals of both sexes was 8 pounds (13-6).
Averages of 23 adult females: Total length, 625 millimeters (660597); tail vertebrae, 59 (76-48) ; ear from notch, 161 (173438); hind
foot, 141 (150-133). The average weight of 55 adult females was 9
pounds (13-6.4). Excluding the females which were advanced in
pregnancy, the average weight was 8 pounds (10-6.4). It is worth
noting that the smallest (probably youngest) female recorded as an
adult was already pregnant. On the other hand more than one nonpregnant female was recorded at 10 pounds.
Averages of 30 adult males: Total length, 619 millimeters (670-553) ;
tail vertebrae, 57 (70-52) ; ear from notch, 163 (173-146) ; hind foot,
140 (150-127). The average weight of 61 adult males was 8.2 pounds
10.5-6).
On the above showing" size and weight differences between the sexes
are insignificant.
478
TECHNICAL BLLLBTIN
No. 49
THE ARIZONA JACK RABBIT (LUPUS CALIFORNICUS
BRUM1CUS)
Average measurements of 32 adult specimens of both sexes taken in
various localities in southern Arizona: Total length, 556 millimeters
(630-465); tail vertebrae, 71 (90-50); ear from nbtch, 139 (163-127) ;
hind foot, 132 (145-112). The average weight of 47 adult specimens
of both sexes was 5.5 pounds (7.5-4.4).
Averages of 20 adult females: Total length, 572 (610-540); tail
vertebrae, 72 (90-50); ear from notch, 136 (145-127); hind foot, 131
(145-112). The average weight of 24 adult females was 5.9 pounds
(7.5-4.4). Ten non-pregnant females were found to average 5.8 pounds
(7.3-4.4) in weight, or almost as much as the whole lot of females.
Averages of 12 adult males: Total length, 559 (630-465) ; tail vertebrae, 70 (90-55); ear from notch, 143 (163-136); hind foot, 133 (145123). The average weight of 23 adult males was 5.1 pounds £6.1-4.4).
Here again, sex differences in size are insignificant.
Dixon (1926), found marked differences of both length and weight
between the sexes of L. c. richardsonn in Kings County, California.
STRUCTURAL ADAPTATIONS IN T H E JACK RABBITS
The jack rabbits are specialized in numerous and important ways.
While we cannot at present go into this phase of inquiry, we believe an
intensive study of their adaptations to environment would be of interest as well as importance. To get the most out of such an investigation close attention should be given to behavior as well as structure of
the animals. There is nothing commonplace about the jack rabbits.
They attract almost instant notice from passersby. Their speed of running, associated with lanky build, long legs, and appropriate musculature, is perhaps the most conspicuous of their characteristics; but their
sensitive hearing, associated with their phenomenally long ears, is only
slightly less so. Among other adaptations deserving mention are their
independence of a supply of free water and their success in hiding their
young.
There is hardly a feature in the structure or behavior of the rabbit
which would not well repay critical study. As a living machine,
adapted to life in an arid environment, the jack rabbit is an outstanding
success.
DISTRIBUTION AND HABITAT
LUPUS ALLENI
Lepus alleni belongs to the subgenus Macrotolagus, and is one of the
so-called Lepus callotis group of white-sided jack rabbits, a group principally Mexican in distribution. Three species and two subspecies are
JACK RABBITS IN ARIZONA
1AVAJ0
479
APACHE
Fig. 1.—Range, in Arizona, of Lepus alleni (shaded area) compared with that of
Lepus califomicus ssp, which occurs all over the State.
exclusively confined to that country, and but two forms, L. alleni and
L. gaillardi, get into the United States. L. gaillardi barely crosses the
line into extreme southwestern New Mexico, while the antelope jack
rabbit (X. alleni) is found over a considerable portion of southern Arizona (Figure 1).
480
TECHNICAL BULLETIN
No. 49
Vorhies, on a trip from Tucson to Port Libertad, Sonora, Mexico,
observed Lepus albnii at intervals all the way, thus extending to the
westward the range of the species as mapped by Nelson (1909, p. 116).
In Arizona L. alleni is found north to Queen Creek and to a point
half way between Sacaton and Chandler (Maricopa County), east to
Cascabel, Pantano, and Empire Ranch (Pima County,* and west to Quijotoa Valley, Ouitobaquita (Pima County), and Casa Grande (Pinal
County). Southward this jack rabbit is found to a little beyond Guaymas, in southern Sonora, Mexico.
The species is exclusively Lower Sonoran. It is found from sea
level to an average altitude of about 4,000 feet. We have one record,
V. R. Ranch, near Rosemont, Pima County, Arizona, 5,000 feet.
The antelope jack rabbit occurs in a variety of situations in Arizona,
seeming to prefer grassy slopes at moderate elevations. The animals
seem to like the bahadas or mesas above the giant cactus belt, where
grasses, mesquites, and catclaws abound. They occur also, somewhat
scattered, on the creosote desert, and even, at times, in the heavy mesquite growth along the valley bottoms. On the grassy bahadas at altitudes of perhaps 3,500 feet, the antelope jack rabbits are usually several
times as numerous as the Lepus californicus type; but in the mesquites
along the valley bottoms, and on the barren creosote bush desert, the
L. calif ornicus type is usually more numerous. Lepus alleni is rarely
observed in broken or hilly country.
We are unable to determine the factors limiting the distribution of
the antelope jack rabbit. Altitudinally and zonally temperature may
possibly control. In general, the grass is both more dense and of
greater volume above the point at which L. alleni stops. There is often
a better supply of other food, also, as mesquite and other herbage. Habitats apparently suitable extend to the north, in the direction of Phoenix
and Wickenburg, well beyond the last antelope jack rabbit. There are
no appreciable physical or climatic barriers except to the westward. In
the vicinity of Gunsight, Pima County, the soil and vegetation change
somewhat, the soil becoming softer and more sandy. Some mammals
occur in the sandy soil to the west which are not found in the harder
soil to the east (Vorhies and Taylor, 1922, p. 9). The vegetational
change as a barrier is difficult to define, but to the westward throueh
this region there is less precipitation, and succulents, on which the jack
rabbits would have to depend more and more for water, become less and
less abundant. The limit of distribution to the westward is less puzzling than in other directions. In the vicinity of and for some distance to the east of Pantano the grass cover becomes much iniDroved,
and there the antelope jack rabbit drops out.
* Recently observed by the authors east to near Fort Huachuca, Cochise Countv.
JACK RABBITS
IN ARIZONA
481
The occurrence of antelope jack rabbits on the Santa Rita Range
is very spotty. They frequently congregate in places where mesquite
is thick and grass correspondingly reduced. The animals are more
abundant than elsewhere over a certain tract, several square miles in
extent, centrally located in the mesa type in Pasture 2 of the Range.
The grass on this area is scattered and the noxious burroweed, (Isocoma
coronopifolia)* is abundant. Mesquite and other shrubs are present in
moderate abundance. There is a "lick" in this area, where rabbits evidently go to eat soil. The poor character of the grass on certain areas
of rabbit concentration may be due in part to soil conditions and overgrazing by livestock, and in part to grazing by the rabbits themselves,
it is entirely possible that overgrazing by livestock has reduced the grass
and brought on a crop of weeds and that the rabbits have been attracted
by the more open country and perhaps by the more palatable varieties
of these weeds.
At times one finds the jack rabbits abundant on the mesas, at others
in the shallow washes, which ordinarily possess a greater variety of
vegetation than the mesas. The jack rabbits may therefore at times
find better food and shelter in the washes, and there, during the heat
of the day or when a wind is blowing, they tend to congregate.
T H E LEPUS
CALIFORNICUS
GROUP
The he pus calif ornicus group, also of the subgenus Macrotolagus, is
made up of the so-called gray-sided jack rabbits. To it belong £,. californicus with 14 subspecies and L. insularis of Espiritu Santo Island,
Lower California. The members of the L. californicus group constitute
the typical and well-known jack rabbits of the western United States
(Nelson, 1909, p. 127). They range from South Dakota and eastern
Washington south to the Valley of Mexico, and from the plains of Kansas and Texas west to the Pacific Coast. Altitudinally the group occurs
from sea level to 8,000 feet or more in the Valley of Mexico and the
mountains and plateaus of our own arid interior. The range of the
species embraces every life zone from the upper border of Arid Tropical through the Lower and Upper Sonoran well into the Transition
Zone. In its flexibility of geographical, ecological, altitudinal, and
zonal requirements, the h. calif omims group of jack rabbits stands in
vivid contrast to the group of white-sided species.
Information gathered within the ranges of the several subspecies of
Lepus calif ornicus in the Sotithwest has been entered under the species
rather than the subspecies. Data available are not sufficient to war* Dayton (Misc. Pub. 101, U. S. Dept. Agric, 1931, p. 157) uses Aplopapptu
fruticosus for the burroweed.
482
TECHNICAL BULLETIN
No. 49
rant an attempt to treat the subspecies separately, although this is desirable and ultimately may be imperative. The subspecies concerned
are:
Lcpus calif oniicus desertkola, type locality west edge Colorado Desert,
California. Range: Southeastern California, the greater part of Nevada,
western Utah, western Arizona, and northwestern Sonora.
Lcpus cahfornicus eremicus, type locality Fairbank. Cochise County,
Arizona. Range: Southern and southeastern Arizona.
Lepus californicus iexianus, type locality probably Western Texas.
Range: Northeastern Arizona, southwestern Colorado, New Mexico
except northeastern corner, western Texas, and a considerable area in
northern Mexico.
Lepus californicus melanotis, type locality Oklahoma, near Independence, Kansas. Range: Northeastern New Mexico, northern Texas,
eastern Colorado, most of Nebraska and Kansas, and western Oklahoma.
Lepus calif ornicus merriami, type locality Fort Clark, Kinney County,
Texas. Range: Southern Texas and northeastern Mexico.
GENERAL HABITS
GREGARIOUSNESS
Whether or not jack rabbits may properly be spoken of as gregarious
we frequently see groups of from two to six individuals, especially of
antelope jack rabbits, in suitable places and at all times of the year. In
many cases these groups are undoubtedly associated for breeding purposes, for one or more males may be found in the vicinity of a female.
In other instances, groups are of a single sex.
As an example of concentration, Foster told us of seeing on one occasion 17, and again 25, antelope jack rabbits in one bunch near Batamote Ranch, Sierrita Mountains, southern Arizona.
On February 24, 1928, antelope jack rabbits were abundant on the
slopes of certain washes on the Santa Rita Range. Between 5 and 6:30
p. m. 4, 6, 10, 12, and even 20 of these rabbits were observed, scattered
well out over the landscape, and finally, by carefully scanning the area
panoramically from one point, 32 were seen. These were not bunched,
but well scattered out. Nearly all were feeding or watching; very few
were resting.
Between 3:30 and 4:00 p. m., February 20, 1925, few antelope jack
rabbits were found on the mesas of the Santa Rita Range. A count
made over a 2-mile course disclostcNonly seven individuals, but in a
JACK RABBITS IN ARIZONA
483
certain large wash they were abundant. Apparently the rabbits had
resorted to the wash to escape the effects of a strong wind. Groups of
half a dozen or more rabbits were commonly observed. Sixteen ran out
from the wash onto the mesa at about the same time. In a few minutes
SO were counted in the wash, and in half an hour about 100 were seen.
Observers in a different part of the wash reported similar large numbers.
For years it has been noticed that in another tract in a protected wash
on the Santa Rita Range, the antelope jack rabbit seems usually to be
present in fair numbers, even when scarce elsewhere. A particularly
notable concentration was evident in January and February, 1931, when
between SO and 100 individuals were observed on 10 acres. The animals
were abundant in this area through January, February, and March, except once in March when they were nearly all absent; but they appeared
again in somewhat reduced strength the following week. During this
period counts of rabbits were being conducted all over the Range, and
no other concentration of so large a group was discovered. By April 21
this aggregation had broken up. Such concentration in this area was
conspicuously absent in the corresponding months of 1932.
DAILY MOVEMENTS
Where food and shelter are available in one place, no major daily
movement of the jack rabbits occurs. Thus during January, February,
and March, 1929, Aldous found the animals remaining in the mesquite
and blackbrush areas of the Jornada Range, where they enjoyed excellent protection, and where, at the same time, food was available. Probably little movement occurs anywhere when grasses and brush are found
together in fair mixture. The rabbits obviously move out from shelter
into the small open spaces in late afternoon, say from 4 or 5 o'clock on,
and can be seen there in the early morning hours before they retreat
to their near-by forms for the day.
But when "food areas" and "shelter areas" are separated by some
distance, a morning and evening migration may be readily observed. It
is frequently the case that brushy areas suitable for shelter have scant
grass or other food, while tracts where food is abundant are short on
shelter. The amount of jack rabbit movement varies in accordance with
the distance between these areas. It may mean merely travel from
brushy washes to near-by grassy mesas, but often succulent grasses and
herbs are found on valley floors at some distance from brushy refuge.
Daily movements of 1 or 2 miles each way must be fairly common. In
dry seasons migrations of 10 miles round trip from desert to alfalfa
484
TECHNICAL BULLETIN No. 49
fields are known. At such arid periods jack rabbits characteristically
invade the outskirts of desert cities and towns, moving onto green
lawns in late evening and doing some clipping of roses, hedges, and
similar ornamentals. The suburban householder, rising at dawn, may
find a number of big hares industriously clipping his grass. About sunrise they begin to move off, particularly if disturbed by passing cars.
Similarly from other feeding grounds there may be seen in early
morning a rather leisurely jack rabbit migration back to the brushy
areas. Nursing females regularly move to their young at night, and
away from them in the daytime (see p. 505).
Times of leaving and seeking shelter vary not only with individuals
but with the kind of weather and time of year. In hot, sunny, summer
weather jack rabbits look for the shade at least by 8 or 9 o'clock in the
morning. If forced to sit out in the sun at midday, as when being
closely followed for observation or photographing, they are noticeably
uncomfortable. This discomfort in the midday sun may be noted as
early as late March, and is not surprising, since the soil surface on
the Santa Rita Range attains maximum temperatures of 120° F. to
130° F. at this season, rising in June to maxima of 150° F. to
160° F. In January or February, on the other hand, many jack
rabbits may be seen basking and dozing in the warm sunshine,
even at midday. The soil surface maxima on the warmer days of
January and February, 1931, ran between 80° F. and 90° F. with
two days for short periods at 93° F. and 95° F. On cloudy summer
days jack rabbits are likely to be seen in the open at any hour of the
day, but on such days in winter, particularly if a chill wind be blowing,
they hunch down close in the best sheltered forms accessible and are
difficult to see.
SEASONAL MIGRATIONS
We have not observed any distinct or regularly recurrent seasonal
migration in either species of jack rabbit in southern Arizona, a fact
possibly correlated with the absence of a severe winter climate.
Gorsuch, in residence for some months near the old Parker Ranch at
the upper border of the Range, noted few or none of either species early
in May, 1931. From that time to the last of June, when the grass had
come up well, the numbers of jack rabbits appreciably increased. It
seems obvious that jack rabbits must frequently move in response to
growth of succulent vegetation.
In autumn, 1927, Nichol noticed that californicus was abundant on
JACK RABBITS IN ARIZOXA
485
the foothills northeast of Vail. A check-up in December showed the
same area practically free of jack rabbits. Snow had fallen recently in
the hills, and a sharp cold spell had followed, and we can only surmise
that the rabbits had moved to a lower, somewhat warmer region.
Hollister, at Mojave, California, did not see a single jack rabbit from
January 9 to February 5, 1905. He was told they were plentiful in
summer and fall but always scarce in winter. That they had some time
been abundant he verified by "plenty of old sign."
Bailey found the distribution of califoniicus in New Mexico in August, 1908, more or less dependent upon the presence of green food.
The rabbits left the dry and barren valleys or slopes that the rains had
missed, and gathered in numbers in other sections where green grass and
succulent plants were available. These seemed to be local migrations or
wanderings, comparable to the drifting of stock to the best range.
By all odds, the most definite and striking record we have seen of
jack rabbit migration comes from Oregon, where Gabrielson in Malheur
County, December 21, 1921, reported observing a very considerable
movement of the animals. While he was traveling in a blinding snow
storm at a low temperature from the high country to the north of Ontario 6 miles towards Ontario, thousands of rabbits were seen, all traveling down hill. They were all moving" into the face of this storm and
all going in the same direction. Neither Oabrielson nor those with
whom he talked had ever seen anything like it.
Jack rabbits make conspicuous trails. These may indicate local movements, perhaps nocturnal, of which we know little or nothing. On a
certain ridge of the Range there is an unusually well-marked trail extending for some distance along the crest. On approach of an observer
several to many antelope jack rabbits, when frightened at a distance,
may be seen coursing along this trail, always going down the slope away
from the mountains. Thirteen individuals have been seen thus in a
single file. The tendency on the part of the antelope jack rabbits on
the higher parts of the Range to move down grade when alarmed is
characteristic. The animals leave the neighborhood only temporarily,
however, for observations on succeeding days show undiminished numbers present.
E X T E N T OF HOME RANGE
Information on the home range of rabbits is disappointingly meager.
It is somewhat surprising to be forced to realize that so wild and free a
creature as the jack rabbit may have a definite home range at all As
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TECHNICAL BULLETIN
No. 49
one ordmarih sees the animal, running across country at the rate of 25
to 40 miles an hour, he gets such an impression of limitless liberty that
it is difficult to feel that the jack rabbit is in any way restricted.
On the other hand, the obvious concentration day after day of rabbits in particular places, often of relatively small size, indicates a degree
of localization, and there is no doubt at all that some individuals at least
return even to particular forms (see p 504). An observer once followed an indn idual of Lepus alleni at a respectful distance, so as not
to alarm it, for an hour and a half The animal remained in an area
perhaps 500 feet on the side. It seemed very definitely to prefer to stay
in the same general locality.
Seton (1929, pp. 704-705) found the home range of the snowshoe
rabbit (Lepus americanus phaeonofus) to be very small. He believed
that in thick woods the home range was not over 20 or 30 acres, in more
open woods perhaps twice that. One of the animals, under Seton's
direct observation, spent all summer within a radius of 100 yards. It
could not even be driven from this limited area Grange (1932, p. 5)
also gives evidence for his belief that the snowshoe hare has a restricted
home range. In one case this was estimated at 10 acres, and several
similar instances were noted
From long observation of jack rabbits on the Santa Rita Range,
however, we have foimed the opinion that their home range in that
locality may be several miles in diameter It is not improbable that
californicus, ordinarily an animal of the open plains, has an extensive
home range, and alleni, of large size and a dweller in arid lands, perhaps
an even more extensive one.
ATTITUDES AND MOVEMENTS
The attitudes and movements of the antelope jack rabbit, whether
resting, feeding, playing, fighting, or running from an enemy, are decidedly more spectacular than those of the Arizona. At times, the animal sits or| its haunches in the form, fore feet down on the ground in
front of it. From this position it can make a sudden leap and a very
very quick get-away. When more relaxed, the rabbit crouches low in its
form (Plate 2, A) folding its fore legs back under the front part of the
body, the backs of the fore feet down, the palms up. In this case, the
animal must needs rise to the palms-down position before starting off,
and a slight alarm brings this response.
The ears, as the jack rabbit rests or dozes, are laid along the back in
a relaxed position. At slight alarm, the animal rises to a leaping posture and brings up the ears to a position of attention. If it decides to
488
TECHNICAL BULLETIN No. 49
trust to concealment rather than flight, it hunches down lower than ever
in the form, pressing the ears tightly against the back. We have frequently seen rabbits in the distance, ears erect. As we approached the
ears were slowly lowered, like a semaphore block signal, the rabbit
"freezing" and becoming very inconspicuous. Lepus alleni frequently
crouches or rests at ease flat on its form with fore legs extended, and
sometimes in the open stretches out lazily, flat on one side, to bask in
the sun like a cat (Plate 2, B). Such an off-guard posture in so timid an
animal is surprising. Occasionally an antelope jack rabbit may be
closely followed for 2 or 3 bou s at a time, becoming almost indifferent
to the presence of the observer, and carrying on its activities in an
apparently normal manner. It has been possible to observe one dozing
in its form and in the (winter) sun; gathenng itself in readiness for a
sudden start; taking a long, lazy stretch when made to leave its form
unwillingly, but not greatly alarmed; feeding; washing its face; extracting thorns from front or hind feet; rolling in dust or sand (Plate 2, C) ;
and in all stages of flashing the white rump
Lepus californiats in southern Arizona is very much the more timid
of the two species, and we have not been able to observe it so closely.
THE RUMP-FLASH
Of all the remarkable features possessed by the antelope jack rabbit,
the rump-flash is one of the most spectacular. When this rabbit runs
away from an observer, a conspicuous white area shows up on the
rump, appearing to shift each time the animal turns, the white being
kept toward the observer, partly by the manner of holding the skin and
partly by the zigzag course taken by the running rabbit. This is the
rump-flash from which the white-sided jack rabbits take their name, and
which is responsible for the term "antelope" as applied to L. alleni.
The white on the rump is flashed by a set of skin muscles that pull
the skin of the hind quarters over the back and up on one side at the
same time everting the hairs, thus exposing a surprisingly large white
area on the left or right rear as the case may be. The hindward part of
the median dark band of the back is thus thrown in a curve to right (or
left), the diagonal position of the posterior end of this curve being continued by the black of the tail which is held down and thrown diagonally
to the left (or right). The movement of the skin (which is much
looser than in californicus) and hair can be readily simulated in a freshly killed animal by stroking the skin of the flank and rump up and over.
When startled, an antelope jack rabbit ordinarily flashes the white and
JACK RABBITS IK ARIZONA
489
is off so quickly that the details are not readily observed. Occasional
individuals which can be followed closely will move about at their feeding or hop slowly away from an intruder without flashing the white, or
will shift the skin partially or slowly and let it return to resting- position without running away. The psychology of this movement seems
fairly evident. Whatever else it is the rump-flash is clearly a fear
reaction. The jack rabbit that is startled usually flashes the signal and
starts to run the same instant, and continues the flashing so long as it
is sufficiently frightened to run. Individuals hopping about to feed, or
running but not alarmed, as in play or chasing each other, do not show
the white. Those observed at close range will sometimes flash if suddenly startled even though not sufficiently frightened to run away. A
jack rabbit may start from its form with white showing, make one or
two leaps and stop. While it remains poised for flight the white shows;
if it relaxes its nervous poise and settles back to a sitting position, the
dark mantle is lowered and the white disappears. With a reasonably
tame individual one may almost cause the flashing or prevent it at will.
The animal in flight never runs straight away, but follows a zigzag
course usually keeping the white of the rump toward the pursuer.
The use of the rump-flash, if it has a use, is decidedly uncertain. By
some of those not familiar with it the rump-flash is generally believed
to be a directive signal by the rabbit to its fellows: "This way !" perhaps
also a warning to predators that "This is one of the fastest of the jack
rabbits — no use to follow!" Perhaps the rump-flash serves to inform
other rabbits of approaching danger. The flash may help to confuse a
pursuing enemy. When a quick change is made from the brilliant white
rump to the darker "normal" coloration a pronounced obliterative effect
is observed.
But the problem is confusing. One wonders why the rump-flash as
a directive feature would not serve to attract the attention of predatory
enemies equally as well as jack rabbits; and on the other side, why the
obliterative effect would not tend to conceal the rabbit from its own
kind as well as from predatory enemies.
RUNNING, JUMPING, AND SWIMMING
The running movements of Lepus alleni and Lepus californicus are
so different that one familiar with both species can usually distinguish
them at a distance, particularly when in full flight. Alleni bounds boldly
away, often into the open, making a longer, higher, "observation" leap
about every fourth to fifth jump. The leisurely moving, unfrightened
individual which is not "flashing" does not make these observation leaps.
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No. 49
Lepus californicus, while it may leap over small bushes or similar obstables, is more prone to "sneak" away without making itself conspicuous by long leaps, and even when frightened pursues a flatter course,
not bounding so high from the ground in its observation leaps.
Speedometer tests show that probably both species of jack rabbits
readily attain speeds of 30 to 35 miles an hour. Lepus alleni, at least,
is capable of higher speed on rare occasions. One of these big jack
rabbits was found inside our 2-acre rodent-proof exclosure, which is
fenced with hardware cloth 3 feet high. This rabbit was being chased
to learn whether it could or would jump over the fence. It finally
became much excited and headed directly for the fence at high speed,
giving an impression of being stretched out low and parallel to the
ground like a greyhound. This individual certainly ran faster than
those measured at 30 to 35 miles per hour. It evidently did not see
the fence, made no effort to leap over it, struck the hardware cloth
squarely and was thrown back 12 or 15 feet with a broken neck. Efforts
to induce similar bursts of speed on the part of rabbits in the open have
always failed. We have, however, seen one of these animals clear a
fence 5^4 feet high with an easy bound. Ordinarily, however, netting
2l/i feet high suffices to exclude jack rabbits.
Naturally, jack rabbits in arid regions have little necessity and few
opportunities to swim. On one occasion an Arizona jack was observed
to cross voluntarily a shallow stream, where two leaps in the water were
necessary. Another was seen to land accidentally in shallow water obscured by a surface layer of duckweed. This individual, though frightened, leaped back to shore rather than swim across the narrow arm of
still water for a direct get-away.
SENSES
Of the five senses, only three, sight, hearing, and smell can be discussed, and these only in a fragmentary way. Nothing can be said of
the sense of touch save that the vibrissae on the nose are long and sensitive, and may be assumed to be useful tactile organs. The sense of taste
must aid in the selection of the rabbit's food froin a bewildering array
of available plant life, but even here, the sense of smell plays an unde«
termined and probably important part.
With such enormous ears, one would assume the jack rabbit's hearing
to be keen; and observations in the field bear out the assumption. Jack
rabbits at times leave their forms and take to flight at such distances in
advance of the observer, and under such circumstances, that the only
JACK RABBITS IN ARIZONA
491
tenable hypothesis is that they have heard his approach. Intervening
brush or other objects may cut off the view, and a breeze coming toward
the observer may eliminate odor, yet the animal senses his coming and
escapes. The movements of the ears are precisely those which we
have learned to associate with their use in animals of keen hearing.
The nose, like that of the domestic rabbit, is continually in quivering
motion, giving an impression of sensitiveness which is borne out by field
studies. While we are accustomed to associate the keenest olfactory
sense with carnivores, it does not necessarily follow that this sense is
any less keen in the herbivores for those things which are important in
their lives. While the jack rabbit does not need to trail or stalk an absent animal to secure its food, it evidently does make its first and often
apparently its sole test of a plant through the sense of smell. If the
odor is satisfactory it tastes, if not, it refuses to eat. Furthermore, the
presence of anal glands indicates the possibility that the jack rabbit may
recognize or trail other individuals of its own species.
The eyes of the jack rabbit are large and luminous, (shining pink in
a white flashlight in the dark), but apparently of little use for distinguishing still objects or details. Movements quickly catch the attention
of the animal which, crouching in its form, watches the approach and
particularly the activities of a suspected enemy. While man is more
fearful of the approach of an object indistinctly seen, the jack rabbit
(particularly Lepus alleni) can often be closely approached from the
obviously incomplete shelter of a bush or cactus, while a step in the
open causes immediate flight. Whether this is due to more discriminating vision in man or to differences of imagination one cannot say. Movements are, on the whole, less alarming to the jack rabbit than sounds. A
young caged Lepus californicus did not seem to find things so much by
sight as by smell. When its water can was placed before it the rabbit
did not seem to see it (recognize it by sight) but approached it in a
gingerly manner, ears forward, apparently trying to hear or smell it.
When the rabbit approached the water closely there was no further difficulty and the animal plunged its nose into the water and drank like a
horse. The same gingerly approach was observed when fresh alfalfa
was put in the rabbit's cage.
BREEDING HABITS
Information on breeding habits in Arizona has been secured almost
wholly by examination of specimens killed in the regular course of our
study, or during rabbit drives.
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No. 49
LIFE SPAN
The length of life of a jack rabbit is unknown. No data are available for estimating it by comparison, since the life span even of the
domestic rabbit is not definitely known. Klugh (1926) says the snowshoe rabbit is "believed to live for eight or nine years/ 7 Probably few
individuals live out the normal life span to perish of old age, as enemies
or disease account for the vast majority.
The age at which breeding begins can be arrived at only indirectly. In
July and August individuals appear which seem to be full grown, but
which when killed and weighed are found to be below average weight,
to have a juvenile appearing pelage, and to show no indication of breeding, or, if females, of ever having bred. Such virgin females, assumed
to be very early young of the year, are not uncommon in late summer
and autumn when practically all other females are in some stage of
breeding. Occasionally such individuals, probably young of the previous summer or autumn, are found in the spring months. One specimen (Lepus calif ornicus), reared in captivity, was kept until past 11
months of age and only then assumed an appearance of full maturity.
It seems doubtful, therefore, whether breeding occurs under one year of
age. It is possible that an individual born in January may breed the
following August, but since it would be scarcely 7 months old this does
not seem probable. All wild jack rabbits born in a given calendar year
may well breed sometime during the next year. Such an age of first
breeding would be closely comparable to the findings of Hammond
(1925, p. 25) in the domestic rabbit.
SEX RATIO
We have recorded the sex of 482 specimens of Lepus alleni. Of these
253 were females and 229 males, a ratio of 52.5 percent females to 47.5
percent males.
For Lepus californicus our records show the sex of 237 specimens:
123 females, and 114 males, or a ratio of 51.5 percent to 48.5 percent.
These figures show no significant preponderance of one sex, and even
such slight differences as appear might well be wiped out if our records
were complete. We are not certain that every male specimen was recorded; most likely not. Sometimes when in the field primarily for
breeding records, and where time or facilities were lacking for measuring, weighing, and recording all the material, some male specimens may
have been disregarded. Occasionally data were hurriedly taken from
chance specimens killed on hunting trips or field work in other lines. On
such occasions we were more likely to record females than males.
JACK RABBITS IN ARIZONA
493
BREEDING SEASON AND RATE
The breeding season of the jack rabbits of the southern Arizona region is one of the longest known. Pregnant females of both species
have been taken during- 10 months of the year (December to September). Females suckling young have been taken in one additional month
(October). This leaves but one month (November) out of the entire
year when all indications of breeding are absent. Obviously a record
by months is required, and Table 1 presents the data for Lepus alleni.
6
ft
Not
breeding
Pregnant
Breeding
Percent
breeding
TABLE I.—LEPUS ALLENI, BREEDING* FEMALES, BY MONTHS.
January
10
4
2
6
60
February
17
1
IS
16
94
March
33
7
22
26
78
April
32
8
19
24
75
May
19
3
16
16
84
June
38
0
29
38
100
July
10
0
9
10
100
August
16
0
9
16
100
September ....
17
4
2
13
76
9
0
0
9
100
November ....
19
19
0
0
0
All evidence of breeding absent.
December ....
14
13
1
1
7
1 pregnancy, but on
last day of month
234
59
124
173
74
Month
October
Totals
Remarks
Young females, full
grown, non-breeding,
began to appear here,
but were omitted
from calculations
when recognized.
Suckling, but no
pregnancies.
* Breeding means any definite indication of breeding such as suckling, or congested uterus, and includes pregnancy.
TECHNICAL BULLETIN No. 49
494
Table 2 gives the records on rate of increase, showing not only the
number of young per litter, but the litter averages by months. The averages of litters by months have at least a suggestive significance, although the records for some months are few. The higher averages are
in those months in which, usually, forage conditions are best, particularly
as regards fresh green grass and weeds, which naturally appear at seasons of greater precipitation. Two rainy periods a year are characteristic of the southern Arizona region, one in winter (December-March)
and one in summer (July-September).
Total
young
Av. per
litter
1
1
2
3
1.50*
11
4
15
19
1.26
10
4
3
22
49
2.22
April
5
5
9
3
2
19
40
2.10
May
10
5
1
16
23
1.43
12
14
3
1
3
1
2
4
4
Females
with 1
young i
Total
females
Females
with 5
young
Females
with 4
young
Females
with 3
young
Females
with 2
young
TABLE 2.—LEPUS ALLBNI, YOUNG PER LITTER BY MONTHS,
Month
January
—
February
March
June
July
-
August
September
1
29
49
1.68
9
28
3.11
1
9
24
2.66
1
2
5
2.50
1
1
1*
124,
241
2
October
November
December
1
Totals
47
50
16
9
2
Percentages ..
3&
40
13
7
1.6
1.93
* T o o few to be significant.
In Table 3 are shown the records of average precipitation for the
region in which the major portion of the litter records were taken, compared with the litter averages by months. Most of the recorded alleni
were taken in the great area embracing both Helvetia (near the Santa
Rita Range) and Tucson. The means of the precipitation records for
these two places, 35 miles apart with a difference of 1,600 feet in elevation, appear to be the logical figures to use. Following the winter
rains, a lag in the appearance of green vegetation owing to low tempera-
JACK RABBITS IX ARIZ OXA
495
tures, might be expected, and actually occurs, a corresponding lag in the
early spring breeding rate being noticeable. The lower average breeding rate in the arid fore-summer (May-June) occurs just where it
might be expected, since most green winter annuals disappear at that
season. There is scarcely any lag in the breeding rate following the
midsummer rains, the summer vegetation springing up with amazing
rapidity.
TABLE 3.—CORRELATION OF PRECIPITATION AND BREEDING
RATE.
Normal precipitation for Tucson (elevation 2400 feet) and
Helvetia (elevation 4000 ft.) on Santa Rita
Litter averages
Experimental Range
by months
Helvetia
Tucson
Lepus alleni
13-year av.
Month
63-year av.
Mean
Inches
Inches
Inches
January ..
1.18
.77
.97
1.50
February-
1.64
,S6
1.25
1.26
March ....
1.27
.74
LOO
2.22
April
.62
.34
.48
2.10
May
.40
.14
.27
1.43
June
.50
.23
.36
1.68
July
4.79
2.48
3.63
3.11
August ....
3.22
2.33
2.77
2,66
September
1.89
1.21
1.55
Z50
October ..
.52
.53
.52
November
.93
.75
.84
December
1.47
1.13
1.30
1
The total number of females taken, while considerable in the aggregate, is none too large for analysis when the two species are segregated;
and if further subdivided according to the months of the year, is only
sufficient to be strongly suggestive of certain breeding tendencies. The
number of breeding females of Lepus calif ornicus recorded is smaller,
and hence less significant and reliable, than of L. alleni The trend
shown, however, by the monthly tabulation (Table 4) of the former is
essentially similar to that for the latter.
496
TECHNICAL BULLETIN
No. 49
January
£:£
34
13
16
21
60
7
100
Percent
breeding
i
C <y
Breeding
Month
Pregnant
TABLE A.—LEPUS CALIFORNICUS, BREEDING FEMALES,
BY MONTHS.
7
0
6
March
27
1
16
26
96
April
21
4
13
17
81
May
12
3
5
9
75
June
14
0
12
14
100
100
February
Remarks
July
2
0
0
2
August
2
0
1
2
100
September
1
0
1
1
100
October
and
November
28
25
0
3
10
Jornada Range; no
pregnancies; three
suckling young.
December
4
1
2*
3
75
All taken between
December 20 and 31.
152
47
105
68
Totals
72
* Recorded on December 24 and December 31.
For 70 females of Lepus californicus we have recorded a total of 157
young, an average of 2.24 per litter. This exceeds the average for
Lepus alleni (1.93 per litter), a species difference which has been in
evidence from the beginning*. The maximum litter recorded was six,
(Table 5), one more than for L. alleni. The breeding rate of Lepus
californicus is 16 percent higher than that of L. alleni if the number of litters per year be the same.
TABLE 5.—LEPUS CALIFORNICUS EREMICUS, YOUNG PER LITTER.
24
24
9
9
2
2
Females
Females
Females
Females
Females
Females
70 Females
(34%)
(34%)
(13%)
(13%)
(3%)
(3%)
having 1 young
having 2 young
having 3 young
having 4 young
having 5 young
having 6 young
each
each
each
each
each
each
24
48
27
36
10
12
young
young
young
young
young
young
157 young
Supplementing these data, Aldous reports the examination of seven
female L. californicus at Willcox, Ariz., April 15-19, 1929, all pregnant.
JACK RABBITS IN ARIZONA
497
Five contained two embryos each, and two but one each, an average of
1.7 per litter. He also noted that there were no pregnancies in "several
females" examined at the same locality January 25-28.
Aldous also contributed data on 32 female L. califoniicus examined
between February 27 and April 11, 1929, in New Mexico (on the Jornada Range, and on a ranch east of the Organ Mountains), which show
a lower breeding rate than our own records. Only one of the 32 was
non-breeding. Thirty-one1 contained from one to three young each, but
with a total of only 46 young, an average per litter of 1.48.
Notwithstanding our rather accurate data on the young per litter and
the length of the breeding season, we are at a loss to determine the number of young per female per year, for unfortunately, the length of the
gestation period in jack rabbits is unknown. Gestation in the domestic
rabbit requires 30 days, but the young are born naked, blind, and helpless. The eyes do not open until the tenth day, and the young are fully
3 weeks old before they compare in size and development with new-born
jack rabbits. Therefore the gestation period of the latter must be
longer. Six weeks would appear to us a conservative estimate of gestation in wild jack rabbits.*
Pregnancies frequently occur while young are being suckled, and in
many cases the litter, even when it consists of more than one, is borne
in one horn of the uterus. In fact, our records show 61 pregnancies
in one horn to 20 in both, and two instances in which litters of four each
were contained in one horn. Eliminating from the 61 those which could
only be on one side (i.e., litters of one only) there remain 31 litters in
one horn to 20 in both. Since the non-pregnant horn of the uterus remains in (or returns to) normal non-breeding condition, and since in
domestic rabbits coitus is allowed at any time during pregnancy (Hammond, 1925, p. 48), it would appear that superfoetationf might readily
occur. Furthermore, the rabbit uterus is primitive, each horn opening
separately into the vagina. Thus the closure due to pregnancy need not
affect both and the unused horn might be open to fertilization throughout pregnancy. We have never found a case of superfoetation, however; in fact, no case is known among wild mammals in which coitus
is permitted during pregnancy. It is extremely doubtful that super* Grange (1932, p, 12) has determined the gestation period of £. a. phaeonotus to
be 36 days.
i Double pregnancy; a second pregnancy occurring before the first conceived
young are delivered.
498
TECHNICAL BULLBTIN No. 49
foetation ever occurs even in the domestic rabbit,Y and it appears to be
extremely unlikely that there is ever any overlapping of successive litters in our wild species. The point is that at least a short period of time
must elapse between the birth of one litter and the conception of another.
Without accurate means of determination of the length of this period,
we reason by analogy that it may be very short, since Hammond with
the domestic rabbit has proved the occurrence of fertile coitus within 24
hours after parturition (op. cit., p. 46). Field observations confirm
this reasoning. We have frequently noted one-sided pregnancies in individuals which were not only suckling, but in which the empty horn
showed clearly that they had but recently had young. Some of these
pregnancies must have occurred almost immediately after parturition.
By no means all of the pregnant females which were suckling young
had conceived the next litter so soon, however, and it would perhaps be
conservative to assume an average of 2 weeks between parturition and
succeeding conception during the active breeding season. In the domestic rabbit the percentage of fertile coitions in the first 4 days after
parturition is much greater (nearly 100 percent) than in rabbits not
recently pregnant (31 percent infertile, Hammond, op. cit., p. 38).
Analogy applied here would indicate a high percentage of pregnancy in
wild rabbits shortly following parturition. Considering the difficulties
of accurate interpretation of these conditions in the field, we believe it
to be more conservative to allow the suggested 2 weeks between pregnancies. This, plus the estimated 6 weeks' gestation period, gives 2
months as an approximation of the time required per litter.
During 8 months of the year pregnancy seems to follow pregnancy
rather regularly. At the rate of 2 months per litter there would be
four litters annually, which at an average of two young per litter would
be eight offspring per female per year. This rate is far lower than for
domestic rabbits and cottontails as well as considerably under the usual
ideas of the general public for jack rabbits. We feel, however, that even
eight per year may be too high, since unfavorable environmental factors,
drouth particularly, through the food supply, doubtless affect the number of young and perhaps even the number of litters. Klugh (1926)
believes that the varying hare, L. americanus, produces but one litter
of three or four young per year. Grange (1932, p. 12) has records on
* Hammond has shown that oyulation In the non-pregnant rabbit follows, and is
the result of, coitus, occurring 10 hours later (op. cit, p. 56). But he has
also shown that in the pregnant rabbit, while the desire for coitus remains, the
act is not followed by ovulation even up to 24 hours, or even 2 hours, before
parturition (op. cit., p. 51).
JACK RABBITS IN ARIZOXA
499
six litters of this species, born in captivity; one of a single young; two
of three each; three of four each. In one instance there were two litters in one season.
SEX BEHAVIOR
Very little information can be secured on sex relations in the field,
first, because the sexes are indistinguishable except by inference from
behavior; and, second, because most of these activities are carried on
during hours of darkness. Frequently one animal may be seen closely
following another in a manner strongly suggesting the following of a
female by a male. On other occasions the following of one individual
by another appears to be the pursuit of a male by a rival male; but
between these more clear-cut instances may be seen many chases even
less susceptible of clear interpretation. Our observations lead us to the
view that both Lepus alleni and L. califonricus are completely promiscuous in their sex relations.
In observations of many hundreds of hares during all daylight hours
we have seen but two completed copulations and two or three unsuccessful attempts, all of L. alleni. One of these coitions took place at
11:25 a.m. on a dark, misty day. The other took place in late evening
just before sundown. The manner of copulation is almost identical with
that of the domestic rabbit. In one case the female, immediately after
completion of the act, chased the male several feet, uttering a peculiar
growl or "grunt." In the other instance a chase and vigorous combat,
accompanied by continuous growling, preceded coition.
VOICE
The jack rabbit is one of the most silent of mammals. When caught,
however, or sometimes when wounded, it cries in distressing tones, and
often quite continuously until released or dispatched. Rarely a peculiar growling or grunting vocal sound, a rapidly uttered "chuck, chuck,
chuck" is made from the throat. On only one occasion have we heard
this from an undisturbed individual, and in but a few instances otherwise, as when fighting or chasing each other.
FIGHTING
Jack rabbits not infrequently stage what appear to be regular boxing
matches. We long believed these to be fights between rival males, and
probably in most cases they are. The contestants rear up on their hind
feet — not merely on haunches — and cuff each other vigorously and
with great rapidity for several seconds, making the fur fly. Usually
500
TECHNICAL BULLETIN
No. 49
these contests are fought out in silence. The fight often ends in pursuit
of the vanquished by the victor. Rarely the combat ends in a draw.
A description of a battle between two Lepus alleni may now be given.
The jack rabbits squared off, opposite each other, reared on their hind
feet, and, with swift pawing motions, went at each other with their fore
feet. After one encounter they dropped down, assumed a nonchalant
attitude, and resumed feeding. The nonchalance, however, was only
for effect. Each must have been trying to catch the other off guard.
Suddenly they again flew to the attack. So absorbed were they that
the observer was hardly noticed. After a short but very brisk encounter, they again dropped back to a position of rest. One pawed a nearby
bush, apparently practicing for the next round ! The third round proved
to be final. The rabbits, now dead in earnest, launched themselves at
each other. They seemed to use, not only their fore feet, but their
powerful hind feet also. The whacking "sput, sput, sput" of paws
striking on body were easily heard. Half a dozen tufts of fur were
dislodged and floated to the ground. The contest became altogether too
hot for one of them, and he made off rapidly, the other close behind.
After pursuing the vanquished one some 75 or 100 yards, the victor
stopped. Soon after the pursued rabbit was seen feeding. Each round
lasted but a few seconds.
Many jack rabbits bear evidence of fights with other rabbits, encounters with enemies, or the thorns and sharp branches of their environment. The ears are frequently torn. One antelope jack rabbit, observed
near Tucson, had suffered near-scalping. A square inch of skin was
torn from the top of the head, the bone being exposed. The wound had
dried up and the rabbit was apparently recovering. Another individual
had suffered a compound fracture of the lower fore leg. The stub had
dried up and was in use, the foot still dangling from it.
The skin on the side of a 6-pound antelope jack rabbit (Santa Rita
Range) had been quite badly torn so that several square inches of raw
flesh were exposed. The wound had partially dried up, but apparently
the individual had small chance to survive.
In March, 1924, near Congress Junction, Arizona, Taylor and Musgrave took a number of Lepus californicus females that had their ears
torn as if they had been fighting. The ears of one were so seriously
injured that the circulation was cut off and most of the pinnae dried up
and lifeless, readily breaking off when handled. Musgrave reports that
jack rabbits fight like bulldogs, bite with their teeth, spar with the fore
feet and kick with the hind feet. Gorsuch, March, 1931, reported observation of a fierce biting fight between two L. alleni
JACK RABBITS
IK ARIZOXA
501
PHYSICAL CHARACTERISTICS IX BREEDING SEASON
N o physical changes sufficiently well marked to be noticeable in the
breeding period have been observed. Close observation is required
even to distinguish females carrying full-term young, and only rarefy
have we been able to do so. T h e mammae are so flatly placed along
the abdomen that they are not noticeable even when most active. T h e
mammillae, on examination of specimens, are readily found on nursing
females. I n both species the mammae are six in number; one pair pectoral, and t w o pairs abdominal.
T h e testes in the males of both species are usually in the scrotum
during the breeding period. These organs are indistinguishable in the
living animal in the field, and only moderately conspicuous when the
animal is killed. I n midwinter the testes are usually withdrawn within
the body cavity, but the inguinal canal is always open and the actual
position of the glands is therefore somewhat variable.
T h e rectal glands, lying in both sexes on either side of the anus,
secrete a substance which hardens to a nearly dry yellow to orangecolored flaky material, with a strong musky odor, somewhat disagreeable at close quarters. T h e characteristic odor of the animal apparently originates in these glands. Each is a simple sack about 12 mm.
deep and with a wide external opening. They do not appear to be any
more active in the breeding season than at other times. Their function
is unknown. I t is possible that by means of these glands the individual
leaves a record in the form or wherever it pauses to sit for a time.
FORMS, NESTS, AND YOUNG
Considering the relative abundance of jack rabbits, their large size,
and the fact that they live in comparatively open country and on top of
the ground, surprisingly little is definitely known concerning their nests
or young. Adult jack rabbits or those of large size almost never take
shelter in any kind of hole or burrow, even when hard pressed or
wounded. We have never seen one do so. Ligon reports that a twothirds grown jack rabbit (X. californkus, New Mexico), badly frightened, entered a large hole in a prairie dog town. Jack rabbits are said
to take to available holes sometimes when pressed by hounds.
Nelson in Jalisco, Mexico, in 1892, recorded the taking of a partlygrown L. cattotis from a, burrow where it had taken refuge from a
caracara. Nelson believed the circumstance indicated that the jack
rabbit had been born there.
502
TECHNICAL BULLETIN
No. 49
FORMS
Jack rabbits of both species habitually rest by day in somewhat sheltered sitting places commonly known as "forms." This term doubtless
was applied first to the places of concealment made by cottontails or
hares backing into or under clumps of grass, weeds, or brush and producing a cavity in the vegetation (and partly in the soil) which fitted
the shape and size of the concealed animals so well as to deserve the
name "form." The jack rabbit is not ordinarily so well hidden as the
cottontail The spot in which it sits varies from moderately well concealed to so open that the name "form" becomes a misnomer, save as
to that part of it which is impressed in the soil. Even the soil impression may be so shallow and inconspicuous as scarcely to be recognized.
W e shall use form, however, for these places regardless of their quality
as hiding places.
At its simplest the jack rabbit form is merely a sitting place beside
a cactus or mesquite trunk on top of the ground where no digging or
scratching effort has been done, and without any vegetative protection.
Sitting in such a form the occupant is in full view from at least three
sides, but is protected from the sight of aerial enemies and sheltered
from the noonday sun. Often the form is dug out so as to be a slight
depression or a somewhat deeper excavation
As a rule the resulting
depression quite nicely fits the haunches of the reposing animal, being
deepest at the rear end and sloping out to ground level at the front.
If beneath a cholla cactus the form is likely to be flanked by fallen
cholla joints (Plate 3, A ) . With the same ground impression the form
may be more or less within some concealing grass or low herbage, or
may be protected by low hanging branches of mesquite or catclaw, or
flanked by standing cactus. Good concealment and protection are
afforded the occasional animal that chooses its form well within the desert hackberry (Celtis pallid a). In such a situation the jack rabbit is
shaded, well sheltered from attack from above as well as from all sides,
and thoroughly protected all around. Most of the forms of L. diem
are found under mesquite, cactus, catclaw, or hackberry, although any
plant of sufficient size to afford some overhead cover is used on occasion. L. californicus uses any of the plants mentioned, but on account
of its habitat, and its somewhat smaller size, makes more use of smaller
shrubs such as burro weed (Iso coma coronopifolia), snake weed (Gutierresia sp.), rabbit brush (Chrysothamnus sp.)» and grass clumps.
Forms (ground measurement) average from 3 to 6 inches wide, and
from 11 to 18 inches in length. In exceptional cases they are longer
or wider. One double form of calif ornicus in the Williams, Arizona,
504
TECHNICAL B L LLB 7 IN No. 49
area, made two arms of a "V77, the rear ends together. Each arm measured 2 feet in length by 6 inches in width, and the deeper one reached
a maximum depth of 3 inches. The depth of the forms generally varies
from the slightest depression to a maximum of iy2 inches. Only in
the deepest of these forms might the occupant find some temperature
benefit in hot weather, and being usually shallow we must suppose
they are scratched out mostly for the clearing of cactus, sticks, and
stones, and a comfortably shaped seat. The forms are so variable that
those of the two species are indistinguishable when not in use, although
in general the forms of alleni are less well concealed than those of californicus. The Arizona jack rabbit (californicus) seldom or never sits
about in the open during midday hours, while alleni does so not infrequently, especially on sunny winter days when it obviously enjoys basking in the sun. At such times these jack rabbits sit out away from any
semblance of a form. In February, 1931, on the Santa Rita Range,
Vorhies saw an antelope jack stretched out on its belly in the sun, and
on investigation found it was lying in a long, trough-like excavation
the size of its body and an inch deep, freshly dug for the purpose
Jack rabbits seem to be by nature too wandering to have a single
form as a home and they probably do not have such a definite abode
for long. There are many more forms than jack rabbits. We have,
however, some evidence that the animals may remain for some time in
the same locality. Vorhies photographed the same ear-marked individual on successive days at the same place, and what was believed to be
a single individual was observed in the same form on at least three
different occasions within a few days.
Klugh (1926) finds evidence that the individual varying hare remains in a very restricted area and uses a single form for a long time.
It is probably not subject to such local variations in food supply as our
arid region jack rabbits.
NESTS
Available data on nesting of jack rabbits are unsatisfactory. While
we feel reasonably certain that Lepus californicus places its young in
nests at birth, we are able only to surmise that L. alleni does so. We have
spent hours of time and much effort, in the height of the breeding season, where the animals are common, searching for nests (or for young)
of L* alleni, without success Two or three quite young jack rabbits
have been found wandering about, but these discoveries seemed purely
accidental. Years of experience in the field prove to our satisfaction
that as one goes about his outdoor business he simply does not see the
JACK RABBITS IK ARIZONA
505
young that are less than half grow n ; and this, even the cattleman daily
on the range corroborates. Forest Service officers and Biological Survey rodent control men also support these statements. Until they are
nearly grown young jack rabbits are more wary than the adults, more
strictly nocturnal and less prone to leave their forms.
Where then, are the young born and reared? L. californicus often
places its young in a prepared nest, more or less completely beneath
the ground level, with some hair as a lining. This accords with observations of farmers who have plowed up nests in alfalfa fields. Gilchrist,
in 1920, found eight nests in an alfalfa field in Salt River Valley, Arizona. These were on ridges ("borders") above the irrigation water,
but were sunk into the ground, level with the surface. Each was thickly
and warmly lined with fur and only a small opening was left at the top
The nests were invisible except when plowed up, evidently having been
closed and partly covered with earth when the mothers left them. Although no old rabbits were seen about the fields they were common out
over the sides of the valley, and it must be that they visited the nests
at night only, to suckle the young.* Musgrave reports having plowed
up perhaps two dozen nests of a like character in eastern Oregon. The
domestic rabbit not only well conceals its young in the nests but can seldom, if ever, be found with them by day. They are probably suckled exclusively at night. Our data on nests from this and other states indicate
that L. calif ornicus usually thus conceals and suckles its young. Sometimes, however, owing to adequate above-ground cover and hard soil,
the nest is hardly more than an enlarged form beneath heavy grass
clumps or brush. Thus, Taylor and Musgrave in March, 1924, west
of Congress Junction, Arizona, found all gradations from surface forms
to excavated globe-shaped nests The forms and nests varied from
circular to elliptical, their dimensions varying from 15 to 22 cm. long,
and from 10 to 18 cm. wide. Some of the forms were merely slight
depressions in the surface, while the nests were excavated to depths of
3 to 11 cm. All were well concealed in the grass.
In spite of our failure/ to find nests of L. alleni, we have three definite records from competent observers. The first two of these, reported
by Musgrave, indicate the same habit as found for californicus. One>
found in 1919 near Arivaca, Arizona, was located under a bunch of beargrass (Nolina).
It was rounded out and covered with bits of beargrass,
was excellently concealed, lined with fur from the mother, and contained
two young. A second, found in 1920 near Magma, Arizona, was located
under a mesquite bush in the edge of a clump of sacaton grass. It was
*They travel considerable distances to and from alfalfa iust for their own food.
506
TECHNICAL BULLETIN
No 49
sunk about 8 inches into the ground, lined with fur, and contained one
young rabbit. In February, 1925, Foster found the third recorded nest
of allcni Its location was unique, being within a hollowed-out shell of a
barrel cactus (Bchinocactus sp.), 16 inches m diameter, which had been
excavated to a depth of about 14 inches. Two young, large enough to
hop around, were in the nest, well covered with fur from the mother.
Owing to the difficult} of locating nests, the suggestion has been made
(Seton, 1929, p. 741) that our jack rabbits may scatter their young
about at birth (Plate 3, B) as the European hare is reported to do
Grange (1932, p. 7) working with the snowshoe hare (L a phaeonotus) has talked with many field mammalogists, hunters, trappers, and
others, and has been unable in a single instance to find an authentic
record of any definite rest In course of his studies six litters of snowshoe hares were born in captivity. In no case was a nest made by any
of the parent hares.
The writers are impressed with the probability that with hepus alleni
the young are scattered out at or very soon after birth, and the young
of L. calif ornicus likewise, though perhaps the latter are left in the
place of birth longer than the former.
HABITS AND DEVELOPMENT OF YOUNG
The discovery of young jack rabbits in the open being so difficult,
such fragmentary data as we possess on their habits have been secured
from individuals in captivity originally secured from slaughtered females. Full-term young of both species have been successfully taken
from such females many times. Invariably, after being freed from the
foetal membranes, when a few gasps have established normal respiration, the young struggle to a sitting posture and in less than five minutes make efforts to nurse. If placed next the mother they quickly find
a nipple, but as the body rapidly cools the milk evidently does not flow
well and the nipple is soon abandoned, though efforts to find a source of
supply are actively continued
The young of both species are fully clothed with hair at birth, their
eyes are open, and they can hop about actively. (Plate 4 ) . Although in
the general gray-mottled coloration they are strikingly similar, the young
of Lepus calif ornicus have the black ear tips of that species, while the
ears of the young L. alleni are white-edged. The very young of the
latter, however, do not show the characteristic white rump of the species.
Almost invariably there is a small but distinct white spot in the center
of the forehead of a new-born jack rabbit of either species, though in
some cases this is hardly more than a few white hairs.
508
TECHNICAL BULLETIN
No. 49
A tiny young Arizona jack rabbit was picked up by Gorsuch (August
13, 1930) under a Mimosa in the grass on the Santa Rita Range. When
touched on the nose the little fellow would rear up on its hind legs and
strike or feint with its forepaws, assuming a very threatening appearance. We unceremoniously dumped the little animal into a box between
some packages. He did not like this, and scrambled mightily until he
got up on top where he could look around. He then settled down comfortably and made no further attempts to escape. We put him in a
spring-floor rat trap for the night. He was exceedingly active throughout the hours of darkness. In the morning he was sitting, apparently
uninjured, unconcerned, and comfortable, in a corner of the cage. Not
having facilities for his care, we released him. He sat quiet and immovable, even when one of us stamped a foot right beside him!
Size at birth * is variable, even within a single litter, but the individual in a litter of one is probably as a rule larger than any one of a
litter of three or four. As it is difficult to secure accurate measurements of living young, our records are fragmentary.
One young Lepus allcni (litter of one) weighed 184 grams the next
morning after being taken. Three individuals from one litter weighed
respectively 108, 103.5, and 90 grams on the day taken. This gives an
average for the four of 121.4 grams, with the largest more than twice
as heavy as the smallest.
Measurements of two of the litter of three (after five days) were:
Total length, each 150 mm ; tail vertebrae, 8 and 8.5 mm.; hind foot, 40
and 45 mm.; ear from notch, 37 and 40 mm.
Two taken in the open estimated as a day or two old were as follows:
To.
1
2
Total
length
155 mm
158 mm.
Tail
vertebrae
25 mm
22 mm
Hind
foot
39 mm.
43rnm.
Weight (2 days later)
133 grains
183 grams
Of californicus, we have complete data for one litter of four compiled
from the living young one day after they were taken.
No.
1
2
3
4
Av.
Total
length
140 mm.
140 mm.
140 mm.
140 mm.
140 mm.
Tail
vertebrae
20 mm.
20 mm.
20 mm.
18 mm.
19.5 mm.
Hind
foot
33 mm
34 mm.
36 mm.
33 mm.
34 mm.
Ear from
notch
30 mm.
25 mm.
26 mm.
27 mm
27 mm.
Weight
65 gram1'
66 grams
71 grams
60 grams
65.5 grams
Since specimens that were naturally bom have not been available we judged
when the foetuses were fully developed by the full-furred pelage, activity, lack
of bleeding of the severed umbilical cord, and other indications of normality.
JACK RABBITS IN ARIZONA
509
From Texas, Bailey has recorded a litter of one taken from the
mother: Total length, 204; tail vertebrae, 26; hind foot, 52; weight 2
ozs. Here again we see the individual in a litter of one exceeding in
size any of a larger litter.
It is not physically difficult to feed young jack rabbits from the first,
as they take milk readily from a medicine dropper and soon become
expert at it. When a few days old they will drink from the tip of a
teaspoon or even from an open saucer. After feeding, which usually
results in smearing the face, the youngster washes its face in the manner of a cat.
From the dietetic standpoint feeding is not simple. We have tried
cow's milk, creamy, ordinary whole, and diluted; and condensed milk
diluted in varying degrees, only to have one little rabbit after another
turn ill with digestive trouble in about 10 days and quickly die. Using
cow's milk diluted with lime water one young L. californicus was successfully reared to maturity. A young Arizona jack estimated to be
three or four days old was found in the open, June 14, 1930, its mother
probably dead, as it was very hungry. Evaporated milk, undiluted, was
used because there was nothing else available, and the young rabbit
thrived until July 8, when it broke a leg in attempting to escape from
a boy fondling it.
Two instincts are particularly noteworthy in the young of either species. One of these, which might be called the "following" instinct, is
exhibited by the young which will follow one about at night. The young
rabbit will respond to movement of a hand or foot on the floor, especially
to a light tapping or patting, similar to the thumping sound which rabbits make with their feet. The animal seems to respond to the sound
alone, though the possibility of seeing the movements may not have been
eliminated. At such times, the ears are held in an erect, attentive, position. Since the young are probably never in contact with the mother
by day, this following instinct may be reasonably interpreted as the response of the young to the coming of the mother at night.
The second noteworthy instinct is that of accepting food only at
night. With all the disturbance of captivity, the young rabbits refuse a
schedule of daylight feeding. By day the young jack rabbit rests
quietly, inactive, crouching in a corner, even though perfectly free to
move about in a whole room or house. It is indifferent to food and can
scarcely be forced to accept any milk. By 4 or 5 o'clock in the afternoon it will take food more readily, but if left undisturbed will not move
from its resting place until about dusk. It then becomes surprisingly
alert and active, plays about its quarters, if sufficiently roomy, or leaps
out of bounds if possible. At night a youngster only a dozen hours old
510
TECHNICAL BULLETIN
No. 49
will leap out of a box several inches deep, but will remain quietly by
day.
Nichol noted that a young Lepus alleni taken on July 8 showed the
rump flash for the first time on July 27 when alarmed and running.
Mary F. Taylor succeeded in rearing a specimen of L. c. eremicus to
adult size. This one when taken on July 10, 1923, weighed 254 grams;
its ear from the crown measured 75 mm. and its hind foot 65 mm. Although it was estimated to be about 3 weeks old, it would pay no attention to either green or dry alfalfa Sixteen days later it still drank milk
greedily but showed some interest in hay. Its weight had increased to
493.7 grams (96 percent increase), and the measurements were as follows: ear from crown, 115 mm (53 percent); ear from notch 95 mm.
(49 percent) ; and hind foot 85 mm (30 percent). These measurements
show that the ears of the newly born young are relatively short, but
increase in size disproportionately during the first few weeks of life
On July 28, the jack rabbit ate some hay, though the staple diet was still
milk. Daily weighings were planned and attempted about this time, but
the animal was so terrified by the necessary handling that they had to be
given up. It was active at night and wore a smooth path along the wire
of its outdoor enclosure. By August 13 it was feeding on green alfalfa,
and was very fond of green six-weeks grama. It did not like dry
alfalfa, but was fond of green mesquite leaves.
When thoroughly alarmed the young rabbit would dash blindly against
the wire of its cage, as if seized by an uncontrollable fear instinct. It
played actively in the early morning. On September 13, when nearly
3 months old, it took milk eagerly in the absence of green alfalfa. It
was still averse to dry feed if more succulent material was available.
The little animal approached food or water in a hesitant way, as if it
were not clearly seen but as if to hear or smell it This rabbit, although
timid, appeared to recognize persons to whose presence it was accustomed, and showed alarm at the approach of strangers even at some
distance. It was often nearly frantic with fear of a dog* even at some
distance, particularly after having been badly frightened by a dog
barking at it just outside the cage. Some months later, however, it
became accustomed to the presence of a neighbor's dog.
FOOD
RABBITS AND VEGETATION
Interrelations between hares or rabbits and vegetation have been given
attention in many places. Important contributions have been made by
the following:
JACK RABBITS IN ARIZONA
511
Clements (1916, opp. p. 150) illustrated degeneration of beechwood
due to rabbits, Holt Down, Hampshire, England. The rabbit concerned
was Oiyctolagus cumculus, introduced into England from the Continent
some time in the year 1100.
Hutchins stated (Baker, Korstian and Fetherolf, 1921, p. 310) that
in England, France, and northern Europe, the rabbit was a constantly
recurring trouble to foresters.
Matthams (1921, p. 227) wrote of some of the significant relations
of rabbits, grass, and weeds in Australia.
Tansley (1922) reported on a study of vegetation of the English
chalk, taking account of rabbit effects.
Orde-Powlett (1923) recorded extensive rabbit damage to sycamores
in England.
Farrow (1925a, p. 135) concluded that biological factors should probably always be included with climatic and soil factors in ecological classification. Farrow pointed out the extreme mobility of the various types
of vegetation owing chiefly to the differential influence of rabbits upon
them. We might say, in comment, that possibly natural communities
were always more mobile than we have recognized. The introduction
by man of an undue weight of animal pressure, as by stock-grazing, has
undoubtedly accentuated this mobility, both speeding it up, and giving
it new, and sometimes rather unfortunate directions.
A landmark in the recent development of bio-ecology is Farrow's
Plant Life on East Anglian Heaths (1925b). Farrow discusses the significant interrelations of rabbits, forest trees, and other forms of vegetation in England.
Allan (1926) discussed the effect of rabbit-grazing on the establishment of introduced plants in New Zealand, following severe burning or
grazing.
Harmful effects of hares and rabbits in English woodlands and game
coverts were studied in some detail by St. Clair-Thompson (1928, pp.
121-131, 150).
Lewis, Dowding, and Moss (1928) thought it probable that the influence of rabbits was greater in Alberta than in England owing to the
long winter and scarcity of food.
Bird (1930) in one of the most important studies made to date of a
terrestrial biotic community, concluded that rabbits were one of the
four important factors tending to retard succession in the aspen park
land of Manitoba.
Kittredge (1929) reported that snowshoe rabbits in Minnesota and
adjacent northern Wisconsin, during 1923, 1924, and 1925 caused excessive losses in forest plantations and to all young forest tree growth.
512
TBCHMCAL
BULLETIN
No. 49
A semi-natural experiment involving rather extensive rabbit coactions
with the vegetation and with other animals was reported by Couch
(1930, pp. 334-336). The European rabbit was introduced on Smith
Island, of the San Juan group, State of Washington, about 1900. By
May, 1924, practically all succulent forage was cropped close to the
ground.
Couch has pointed out that on the Snow Creek burn, Olympic National Forest, Washington, rabbits on some plots damaged 97 percent
of planted seedlings. An examination of this area in 1931 by Couch
and W. P. Taylor, however, showed the injury much less serious than
anticipated.
Johnson (1923, p. 28) reports the jack rabbit to be the worst animal
pest with which the forester in the Great Plains region has to contend.
Burnett (1926, p. 5) suggested that distributional changes affecting
two species of jack rabbits in eastern Colorado were associated with
the invasion of the rabbit's original range by man.
Hanson (1929, p. 61, Fig. 4) illustrated a plot border in a Colorado
sagebrush area (Xaramie River valley) from which the sagebrush was
cleared in the fall of 1927. One side was protected from prairie dogs
and jack rabbits. On the other side the jack rabbits grazed heavily.
A marked difference is clearly shown in the vegetation communities.
It was Hill's opinion (1928, p 91) that in the vicinity of Tucson,
Arizona, heavy grazing by domestic livestock, very noticeably accentuated during recent years by rodents such as the kangaroo rat and the
jack rabbit, was the greatest single contributing factor in the change
from a grass type to a desert type.
At the Great Basin branch of the Intermouritain Forest and Range
Experiment Station at Ephraim, Utah, it was found that plantations of
sweet clover, crested wheatgrass, and other species in artificial seeding
tests were so heavily utilized by jack rabbits which congregated on the
areas and grazed the seedlings that many of the trials were almost complete failures. It was necessary to construct fences around the plantations to exclude the hares.
The annual investigative report for 1930 of the Central States Forest Experiment Station, United States Forest Service, recorded 50 percent of Scotch pine in a new plantation near Columbus, Ohio, damaged
by rabbits. From the director of the station we later learned that the
recovery from rabbit injury has been phenomenal even in instances of
very severe damage. Recent unpublished work of Cooperrider of the
Southwestern Forest and Range Experiment Station indicates a remarkable recuperative ability on the part of conifers, mostly western yellow
pine, injured by browsing of cattle, sheep, or game near Flagstaff, Ari-
JACK RABBITS IX ARIZONA
513
zona. Pearson, Krauch, and Lexen at the same station ( Pearson, 1931)
have further shown this by some excellent repeat photographs. In estimates of rabbit or other damage of the same t}pe the complete stor}
has not been told until the injured seedlings or plants have been followed through for several years. Initial injury may not be so serious as
it appears.
We know little of the original relations betw een the jack rabbits and
the vegetation. We may fairly assume, perhaps, a fluctuating equilibrium between the animals and their plant food. In drouth periods the
plants would undoubtedly be hard pushed by the animals, which in
turn, would doubtless suffer a recession in numbers through lack of
proper food and so permit the recovery of the plants. In all probability,
the plant-animal community, though varying widely, and never twice
the same, did after all maintain a fairly definite status and trend.
The entrance of man on the scene, with his flocks and herds, and his
tendency, often short-sighted, toward immediate conversion of natural
resources into cash, profoundly disturbed the original fluctuating equilibrium, and substantially altered the slow, secular trend theretofore prevailing. Livestock now grazed and trampled the plants until in many
cases the turf was broken up, the soil became exposed, leached, and
eroded, and the way was opened for the incursion of secondary shrubs
and weeds where formerly the climax grasses held sway.
Present-day observations of the coactions of jack rabbits and vegetation must be made with this background in mind. The habitat is
changed, the vegetation modified, the soil altered, the successional trend
interrupted. The present-day situation is a new development; indeed,
there is a different equation in each locality. Up-to-date handling of
the rabbit and other organisms will have to take full account of the local
as well as the general situation. The incidence of damage on a given
area often varies directly with the degree of departure from natural
conditions. Some modifications by man which often result in a "rabbit
problem" are: (1) overgrazing, (2) cutting of timber, (3) reclamation,
i e., introduction of farm crops on wild lands, (4) misapplied control of
natural enemies of rabbits. The obvious conclusion is that modifications
in course of agriculture, range management, silviculture, wild life regulation, and other enterprises involving land use should be held to a minimum.
By far the most serious rabbit effects recorded in human experience
have resulted from introduction of the animals in localities where they
were not native. The Smith Island incident is a minor but illuminating
instance of this. A spectacular demonstration on a well-nigh continental
scale is afforded by the rabbit in Australia.
514
TECHNICAL BULLETIN
No. 49
QUANTITY OF FOOD EATEN
FEEDING TESTS AND COMPUTATIONS
A feeding test made by Taylor on an average-sized wild Lepus californicus affords at least a hint as to the amount of food consumed by
jack rabbits as compared with forage eaten by sheep and cattle.
Data derived from 23 daily feedings with green alfalfa and grama
grass follow:
Grams Pounds
Average amount consumed
307.4
0.68
Maximum amount consumed
631.1
1.39
Minimum amount consumed
146.5
0.32
Consultation with McGinnies and Stanley of the Arizona Agricultural Experiment Station, and reference to Henry and Morrison (1°17,
pp. 667-668) establish the fact that a 120-pound ewe will consume approximately 8 pounds of green feed in a day. At the rate of consumption of feed by rabbits according to the determination given above we
obtain the following:
Number of rabbits required to eat as much green feed as one sheep:
Average rate
Maximum rate
Minimum rate
11.8
5.8
25.0
A 750-pound cow will consume 40 pounds of green roughage in a day.
Prom this we obtain the following:
Number of rabbits required to eat as much gtten feed as one cow:
Average rate
Maximum rate
Minimum rate
58.8
28.8
125.0
Data derived from eight daily feedings with air-dry alfalfa follow:
Average amount consumed
Maximum amount consumed
Minimum amount consumed
Grams
128.1
165.6
107.1
Pounds
0.28
0.36
0.24
A 120-pound ewe will consume approximately 4 pounds of air-dry
feed in a day. At the rate of consumption of feed by rabbits according to the determination given above we obtain the following:
Number of rabbits required to eat as much air-dry feed as one sheep:
Average rate
Maximum rate
Minimum rate
14.2
11.1
16.7
A 750-pound cow will consume approximately 20 pounds of air-dry
feed in a day. At the rate of consumption of feed by rabbits according to the determination given a b o m n e obtain the following:
JACK RABBITS IX ARIZOXA
515
Number of rabbits required to eat as much air-dry feed as one cow :
Average rate
Maximum rate
Minimum rate
71.4
55.5
83.3
The above figures are conservative. In some instances the rabbit
would have eaten more feed if it had been available.
M. C. Smith of the Arizona Agricultural Experiment Station, finds
that white rats eat about 6 percent of their weight of air-dry feed in 24
hours. Of succulent feed they eat at least twice that amount, and
sometimes even more than that. Something like the same percentage
relation of food consumed to weight of animal may obtain in rabbits as
in white rats. By using these figures we can check our previous experimental determination of the "jack rabbit equivalent" of sheep and cows.
The figures follow:
LEPUS CALIPORNICUS
Weights of animals
Six percent of these weights
Average
Pounds
5.47
3282
Minimum
Pounds
4.37
.2622
Maximum
Pounds
7.5
.4500
T a k i n g the amount of dry feed consumed by one sheep in one day as
4 pounds, green feed 8 pounds, and the amount of dry feed consumed
by one cow in one day as 20 pounds, green feed 40 pounds, we derive
the following sheep-jack rabbit equivalent (number of rabbits which
will eat as much as one sheep in one day, either dry or green f e e d ) :
Average rate
Maximum rate...
12.1
S.S
Minimum rate
15.4
The cow-jack rabbit equivalent (number of rabbits which will eat
as much as one cow in one day, either dry or green feed):
Average rate
Maximum rate
Minimum rate
60.6
44.4
76.9
LEPUS ALLEN I
Weights of animals
Six percent of these weights
Average
Pounds
8.062
.4837
Minimum
Pounds
6.062
.3637
Maximum
Pounds
13.0
.7800
Similarly determined, the sheep-jack rabbit equivalent for
alleni is:
Average rate
Maximum rate
Minimum rate
-
&2
-— 5.1
10-9
Lepus
516
TBCHXICAL BULLETIN
No. 49
The cow-jack rabbit equivalent for alleni is:
A\ erage rate
Maximum rate
Minimum rate
41 2
25 6
54.8
The calculated check is not far from the experimental results of
green-feed tests. On the average, the sheep-jack rabbit equivalent for
Lepus calif ornicus is about 12.7, and the cow-jack rabbit equivalent about
63.6. For Z,. alleni the sheep-jack rabbit equivalent is about 8.2, the
ccm-jack rabbit equivalent about 41.2.
Another check is afforded by Matthams (1921, pp. 40-43) who gives
an estimate apparently current in Australia that 12J4 rabbits eat as much
herbage as is required to sustain one sheep. The similarity of the Australian estimate to our own is of interest.
CORRECTION IN EQUIVALENTS
Since on the basis of our figures, Lepus alleni consumes 44 percent
(36 percent mesquite and 7.8 percent cactus) of materials in the taking
of which it does not appreciably compete with cattle, the cow and sheep
equivalents for this jack rabbit require correction. According to figures
previously given (p. 515), the sheep equivalent for the species is 8.2,
and the cow equivalent 41 2. A computation based on the 56 percent of
its food (grasses, etc.) which bring the rabbit into competition with
cattle, shows that, on the average, the antelope jack rabbit will eat but
0.27 pound of dry feed in a day. On this basis 15 antelope jack rabbits
would be required to eat as much as one sheep, or 74 as much as one
cow.
On our figures S9 percent of the food of /,. calif ornicus is of neutral
character, mesquite 56 percent, cactus 3 percent, while but 41 percent
(grasses, etc ) brings it into competition with either sheep or cattle.
Thus, but 0.135 pound of feed of which livestock is thereby deprived is
consumed by the Arizona jack rabbit in a day. This means that 30 Arizona jack rabbits would eat as much as one sheep, or 148 as much as i
cow.
FORAGE CONSUMPTION BY RODENTS
A series of quadrats was clipped in connection with studies made on
Plot 1A,* Santa Rita Range, in an endeavor to make a quantitative
*At plot 1A fences were erected in 1918 as follows* (1) A 4-acre area was inclosed with five strands of barbed wire This fence kept out cattle but permitted the free entrance of rodents of all sorts. (2) A contiguous 2-acre area
was inclosed with one-half inch mesh hardware cloth 3 feet high, with barbed
wire above. This fence kept out cattle, rabbits, and large kangaroo rats.
Smaller rodents, and woodrats which can climb the fence, were not excluded.
The quadrats were located along a transect line through the totally protected
plot, the rodent-grazed plot, and the area outside all the fences.
JACK RABBITS IN ARIZONA
519
determination of the actual amount of vegetation consumed by rodents
(Plate 5 ) . The results are given in Table 6. While Lepus alleni, occasionally Lepus californicus, and Dipodomys spectabilis, occur in the
vicinity and graze over the rodent plot and the outside areas, L. allcni
is chiefly responsible for the consumption of vegetation indicated.
The data are meager and consequently subject to considerable error
but constitute definite indications of a trend. It will be noted that 28.7
percent of all the vegetation, and 38.8 percent of the most valuable forage grasses on this particular area, had been consumed or destroyed by
rodents. Later in the season it is quite possible that the contrasts would
be even greater. Pellet counts (Taylor, 1930, pp. 531-534) taken at
the same time, indicated no concentration of rabbits on the rodent-grazed
plot. The quadrat results do not include browse species or grass cut
by rodents and left lying.
In addition to the quantitative results derived from quadrat study,
evidences of rabbit work on vegetation at the experimental plots are
conspicuous. Rabbits feed on various species of browse, consume cactus, work on weeds, and make excavations for succulent roots, producing effects evident in the rodent-grazed plot, but lacking in the totally
protected plot (Plate 7). Table 7 gives some comparisons.
TABLE 7.—WORK OF JACK RABBITS AT RODENT STATION (1A).
(February 20-21, 1925.)
Rodent-grazed plot
Total protection plot
Many rabbit trails and feces through
the grass.
Rabbit trails and feces lacking.
Clumps of grass smaller, more numerous, grass shorter.
Grass clumps larger, less numerous,
grass taller.
Smaller mesquite branches near
ground chewed off.
Mesquites not conspicuously attacked.
FOOD OF JACK RABBITS AS SHOWN BY STOMACH
ANALYSES
Stomach analyses have proved far more useful in determining food
habits of rodents than anticipated. They must be supplemented, however, by every other practicable type of study of the animal in question,
if a true picture of the food habits of the animal Is to be obtained.
522
TECHNICAL BULLETIN
No. 49
Stomach contents do not indicate the extent of root and tuber consumption by jack rabbits, nor do they give an adequate list of the plants
actually ingested, especially of annuals. Many substances consumed,
as bark (outer and inner) of shrubs, and roots, stems, and leaves of
miscellaneous herbs cannot ordinarily be identified in the stomach. Rabbits are sometimes observed feeding on tiny green plants growing on
the ground. Rabbit stomach examinations give little or no record of
such materials.
LUPUS ALLENI
Analyses have been made of 179 stomachs of alleni for the most part
taken on the Santa Rita Range. All months of the year but one (January) are represented. The food material in each stomach was regarded
as 100 units, and all stomachs were totalled, making 17,900 units. The
units of different foods in each stomach were carefully determined, and
the totals added. (Table 8.) Thus 6,342 units, or 36 percent, of the
food for the entire year were mesquite; 7,988 units, or 45 percent, grass;
and 1,404 units, or 7.8 percent, cactus, with lesser amounts of other
materials.
The food of jack rabbits in the southern Arizona region is intimately
related to the alternating dry and rainy seasons, (see Table 3, Correlation of Precipitation and Breeding Rate, and Fig. 2). Following the
winter rains, when a number of the perennial grasses put forth leaves,
the percentage of grass in the diet markedly rises, while the amounts of
mesquite and cactus consumed decrease almost to the vanishing point.
During May and June, the most arid period of the entire year, the grass
dries up, and is much less eaten, while mesquite maintains a high percentage in the diet and cactus increases. In July and August, following
the summer rains, grass becomes by far the most important item in the
diet, forming 80 percent of all food eaten in July and 84 percent in
August. Mesquite falls to its lowest point for the year at this period
of maximum grass development, and cactus also decreases. Through
the fall months the proportion of grass in the diet declines somewhat,
while that of mesquite increases, approximately in inverse proportion.
While deciduous, the mesquite does not shed its leaves in early autumn;
in fact some leaves remain on individual trees all winter.
Cactus does not appear in the stomachs in anything like the quantity
anticipated. In a general way the cactus graph follows that of mesquite. The most cactus is consumed, apparently, in winter, when the
grass is drier than at any other time of year except the arid fore-summer (May-June).
524
TBCHXICAL BULLETIN No.
Grass
Mesquite
36%
6,34-2 units
units
Cactus
Portu/aca
MisceJ/aneouA
45%
7,988 un/ts
7&Y*
67S units
3<
f (Mainly
Boraginaceae,
14-91 units < Scrophu/ar/aceae, Compo$ttae\$ 3%
{ Boerftaa via ancf tfmbrosia )
Fig. 2—Percentage consumption of food of L. alleni throughout the year
Food materials included under uMiscellaneous" in Table 8 are: Portulaca, 3.8 percent (of all food); Boraginaceae, 2.3 percent; Boerhaavia,
22 percent; unidentified Scrophulariaceae, 0.53 percent; Ambrosia, 0.16
percent; Compositae, 0.08 percent; and traces of the following: Afnorpha, Euphorbiaceae, Amaranthus, Briogonum, Mollugo, Sida, Geranium,
Solidago, Malvaceae, a few unidentified herbaceous plant parts, Calandrinia or Oreobroma
( ?), Plantago, Daunts, Atriplex,
Karzvinskia
( ?),
Alsine, Fabaceae, Cirsium, Umbelliferae, Cruciferae, Calliandra, Juncus, Sideranthus, Salsola, Leguminosae, Rosaceae, Artemisia, Pentstemon, Solanaceae, and insect remains. Seeds, leaves, and stems of these
miscellaneous plants are variously eaten. Availability of food materials
and accident of capture of individual rabbits have much to do with the
food found in the stomach.
LBPUS CAUFORNICUS
Analyses have been made of 61 stomachs of calif ornicus, taken principally on the Santa Rita and Jornada Ranges. As with alleni, the food
JACK RABBITS
Grass /f4-7O units
Mesquite
IX ARIZOXA
Zf.1%
3, 335"units
Cactus
Portu/aca
56%
20/ units
•
525
3.3#
iiO units 1.87°
f (Mainly Scrophuianaceae,)
I
M/sce/faneous
j/P1
\iT
W
Am
—•
iE^" JL+ "% ^\
&»
•% &\
I
934 units \ sji^sfda,
Enogonum,, A IUm£m/
and TnJbuit/s terrestns)}
Fig. 3.—Percentage consumption of food of L. californicus erenticus throughout
the year.
material in each stomach was regarded as 100 units, and all stomachs^
were totalled, making 6,100 units (error in one of the office analyses
makes the total 6,110 instead of 6,100, but the results are not affected).
The units of different foods in each stomach were carefully determined, and the totals added (Table 9 ) . Thus, on this record, 1,470
units, or 24 percent, of the food for the year were grass; 3,395 units, or
56 percent, mesquite; and 201 units, or 3.3 percent, cactus. Smaller
amounts of other materials were recorded.
The graph (Figure 3) and Table 9 show that, in these stomachs,
grass and mesquite together made up 80 percent of food taken. Strangely enough, twice as much mesquite as grass was consumed. The
amount of cactus was small; that of miscellaneous plants appreciably
larger than in L. allenk
An inverse relation between the consumption of grass and mesquite
is even more strikingly shown by L. calif ornicus than it is by L. alteni.
526
TECHNICAL BULLETIN
No 49
As in that species, grass consumption has two peaks, one in the months
following the winter rains, the other in midsummer and early fall following the summer rains. In the fall and early winter grass consumption markedly drops. At this period the eating of mesquite reaches
its highest level, declining in the late winter and early spring, inversely
with the winter growth of grass, and reaching a second peak as the arid
fore-summer is approached.
Miscellaneous food items in the 61 L. californicus stomachs included
the following: Amaranthus (seed), Boerhaavia (seeds, leaves), Mollugo (seeds), Compositae (seeds, leaves, bracts), Euphorbia (seeds,
pods, capsules), Pcntstemon (leaves), Tribulus terrestris (fruit), Briogonum (leaves), Scorphuiariaceae, Erodium, Daucus (seeds), Plantago
(seed), Cirshtm (leaves), Astragalus (fruit), Chenopodiaceae, Odosteinon (leaf), Mimosaceae (leaves), Sida (leaves and stems), Cruciferae (pods), Amaranthaceae (seeds), Portulaca (leaves, seeds, pods,
stems, and roots), Artemisia (leaves and twigs), Umbelliferae (seeds),
Atriplex (leaf and fruit), Malvaceae (leaves, seeds), Karwinskia (?)
(seed fragments), Gilia (leaves), Ceanothus (leaves), Fabaceae
(leaves), Silenaceae (seeds), and Ainorpha (leaves).
JACK RABBITS AND BROWSE
Browse is a very large item in the yearly food of jack rabbits. Among
the species to which the animals give attention in the Southwest are:
mesquite (Prosopis), catclaw (Acacia greggii), acacias (A. constrict a
and stiffrut esc ens), palo verde (Parkinsonia microphylla), crucifixion
thorn (Koeberlinia spinosa), soapweed (Yucca elata), chamiza (Atriplex
cancscens), jointfir (Ephedra trifurca), creosote bush (Covillea tridentata), blackbrush (Flourensia cernua), snakeweed (Gutierresia juncea) and Ziayphus sp. (?). Bailey records jack rabbits feeding on Sarcobatus vermiculatus near Kelton, Utah, and Jewett says in eastern
Oregon in winter they feed on sagebrush. In a dry season (June, 1929)
near Seligman, Arizona, Taylor noted that bark and new shoots of
Chrysothamnus were being extensively eaten.
On March 7, 1931, an antelope jack rabbit was seen browsing from
a small burroweed (Isocovia coronopifolia), most of the shoots of which
had been cut off. The observation is unusual, and should not be regarded as indicating extensive work by the rabbit on this poisonous
plant.
MESQUITE
Far more important, in the Southwest, than their effect on any other
species of browse is the work of jack rabbits on mesquite. No other
JACK RABBITS IX ARIZOXA
527
species of brush was present in sufficient quantity to figure in the stomach analysis tables. Mesquite, on the other hand, is one of the principal
foods of the jack rabbits in this region, forming 36 percent of all food
of L. alleni and 56 percent of all food of L. californicus. As already
shown, mesquite is the great alternative to succulent grass. When green
grass is available mesquite is not eaten to any extent. Whenever the
supply of succulent grass declines, the consumption of mesquite increases.
Careful comparison of mesquite trees protected from and exposed to
jack rabbits shows that they regularly snip off many of the lower
branches keeping the trees "aerated." There is no question that, in the
absence of jack rabbits, the mesquites in the Santa Rita region would
be bushier toward the ground. We have seen no evidence, on the Santa
Rita Range, of rabbit work handicapping the growth of mesquite. On
the contrary, Prosopis appears to be thickest where overgrazing by
stock and rabbits is most pronounced. In all probability the work of
jack rabbits favors the growth of mesquite through removal of perennial
grasses. Elimination of competing tufts of these grasses must favor
the establishment of mesquite seedlings.
In browsing from mesquite the rabbit rears up on its hind feet, its
fore feet hanging limp, its ears flopping freely; or, wishing to reach
higher, stands on its toes, places its fore paws on a branch partly for
support and partly to hold down the branch, and proceeds to crop off
leaves, bark, or buds. It is especially fond of the tufts of green leaves
which appear in the axils of the mesquite spines.
During severe seasons jack rabbits may seriously injure mesquite or
other species of browse through gnawing the bark. We have observed
instances where the bark was stripped for a distance of 2 feet. Stems
within 3 feet of the ground and up to 1.5 inches in diameter may be
gnawed. Serious work of this kind is extremely rare. In southern
Cochise County and eastward into New Mexico, the mesquite is of a
dwarf form and some plants occasionally receive attention from jack
rabbits. There is a possibility that where local climatic or soil factors
somewhat inhibit the growth of mesquite, the rabbits also may help to
preserve the dwarf form of the bushes.
Aldous has pointed out that "In sandy areas on the Jornada Range
Reserve, New Mexico, which have been overgrazed the rabbit may
have a beneficial influence on helping restore the range. Where sand
is abundant and overgrazing practiced it is but a short time until the
grass is gone and the sand in a drifting condition. One of the first
steps of a come-back is the growth of mesquite. The small bushes act
528
TBCHKICAL BULLETIN
No. 49
as wind breaks and gradually the sand envelopes a good portion of the
bush. The buried stems send out new shoots and the mesquite clump
increases in size, as does also the sand dune. One of the chief foods
of the rabbit during the winter and spring months is mesquite bark. This
girdling and stripping of the bark naturally injures the plant and it responds like most girdled trees in that new shoots come from below the
sand. The mesquite clump grows and becomes larger and more dense,
thus preventing much of the drifting especially during the summer and
allowing smaller annuals and perennials to take hold. One of the most
important plants in this come-back process is the snakeweed (Gutierrezia
juncea) which makes a good cover over the whole surface. It is among
this snakeweed that the climax grasses, such as gramas, get their start."
OTHER SPECIES
In all probability jack rabbit work is favorable to the spread, not only
of mesquite, but most of the other species of browse. By grazing the
perennial grasses (the chief competitors of browse seedlings) the rabbits, although they may nibble the mature plants and consume some
seedlings, favor the browse species by injuring their competitors even
more. It will be recalled also that aside from mesquite, almost no
browse appears in the stomach analyses. Field observations, however,
show widespread diffuse work on browse.
In drier seasons catclaw (Acacia greggii) is regularly given attention by jack rabbits. Bark may be gnawed from larger stems, the terminal portions of branches consumed, twigs from 1/16 to 1/3 inch in
diameter cut, and small leaf-buds chewed off. A. constrict a also may
be somewhat peeled and girdled. Occasional^ A. suffrutescens is attacked.
While unpalatable in appearance, the terminal branches of the jujube
(Zizyphns), from 1/16 to 1/3 inch in diameter, are snipped off. Even
palo verde (principally Cercidium inter ophyllum) stems from 1/16 to
1/4 inch in diameter may be severed. While ordinarily palo verde is
not eaten, individual shrubs are browsed to a height of 3 feet, and occasionally one finds all accessible twigs gnawed by jack rabbits. Small
bushes, as much as 3 inches in diameter at the ground, may be seriously
injured or even killed. The wood and foliage of hackberry (Celtis pallida) are so tough and repellent that they are given little attention though
tender terminal twigs may be severed. Where it occurs, blackbrush
(Flourensia cernua) is gnawed, but usually not seriously. Small quantities of crucifixion thorn (Koeberlinia spinosa), and soapweed, (Yucca
elata) are consumed. At rather long intervals we have observed rab-
JACK RABBITS
IX ARIZOXA
529
bit cutting on the creosote bush (Coiillea tridentataj; but in southern
Arizona rabbits apparently do not browse this bush. If eaten at all,
the amount actually consumed must be very small in proportion to the
cutting.
W e have observed obvious jack rabbit work on Baccharis
icrightii
(Plate 8, B ) on the Santa Rita Range, where apparently rodents alone
are sufficient to prevent the occurrence of the species under the grazing
conditions prevailing. Bailey reports jack rabbits feeding on the mellow flowers of a trifoliate barberry near San i\ngelo, Texas.
C. P . Wilson (1928a, pp. 19-23; and 1928b, pp. 27-29) has pointed
out the potential seriousness of jack rabbit damage to chamiza (Atriplcx
canescens) under conditions encountered in New Mexico. Wilson asserts that rabbit injury to this plant was frequently greater than that
caused by cattle. Cattle did not nip the seedlings so low, nor were
they so likely to eat the little plants but 3 or 4 inches tall. fi The rather
common habit, with rabbits, of eating only a fraction of the vegetation
that they cut off makes possible greater injury than would otherwise
be the case. They are particularly fond of the larger stems of young
chamizas, apparently not caring so much for the leaves and smaller
stems; many of which are left on the ground where the small bushes
stood before being destroyed." In one set of plot experiments rabbits
and smaller rodents destroyed 72 out of 79 young chamizas (protected
from livestock but not from rodents), while 44 out of 138 young chamizas (totally protected) survived. Wilson believes that chamiza, winter fat (Burotia lanata), and other valuable forage plants would be
found in considerably larger acreage on the ranges of the Southwest
than they are at present if it were not for the depredations of rabbits
and smaller animals. W e wish to point out, however, that this heavy
damage by rabbits is quite likely in part the result of an overgrazed
condition, the perennial grasses having been largely eliminated, reducing the amount of food available. Inevitably rabbit pressure is more
severe on remaining vegetation.
JACK RABBITS AND CACTUS
While the stomach analyses show less cactus eaten by jack rabbits
than expected, nevertheless, the animals feed on cactus in all drier
times of the year.
Not all species of cactus are equally worked upon. The writers have
direct evidence of the eating by rabbits of the following species: OpunHa engelmanii and 0 . phaeocantha (prickly pears) ; Bchinocactus zvis-
JACK RABBITS IN ARIZONA
531
Ikenii (visnaga); Opuntia fulgida and 0 . spinosior (chollas; Bchinocereus fendleri (hedgehog cactus); Mammillaria sp. (pin-cushion cactus, Plate 10, B ) ; Carnegia gigcmtm (giant cactus). Unquestionably
others are eaten.
It is only natural that the least spiny species are most subject to rabbit attack. The prickly pear type is evidently more acceptable than the
cholla (Plate 6, B). On a 4- or 5-mile walk in the Sopori Creek region
(Pima County) 10 chollas and 39 prickly pears were observed. Of the
chollas six showed no rabbit work, one light rabbit effects, and three
serious work. Three of the prickly pears showed no rabbit effects, 8
were lightly and 7 moderately attacked, and 21 of the 39, or 54 percent,
seriously gnawed.
Table 10 gives the results of a much longer count made on the Santa
Rita Range. The plants were examined just as they were encountered
in walking across the country. The table shows that 50 percent of the
prickly pears suffered heavy rabbit attacks, while but 2 percent of
the chollas and none of the visnagas (in this particular count") were
seriously attacked. Some additional counts and observations over a
wide area and through more than 10 years, indicate the essential maintenance of this relationship except that, wherever the jack rabbits get a
chance, they eat visnaga with every evidence of enjoyment.
TABLE lO.^JACK RABBIT WORK ON CACTUS, SANTA RITA RANGE.
APRIL 1, 1925.
Degree
rabbit
work
Prickly* pear
No. of
plants
Percent
Cholla
No. of
plants
Visnaga
Percent
No. of
plants
Percent
Serious*
84
50
2
2
0
0
Moderate
41
24
7
7
0
0
Light
36
21
22
22
4
18
None
5
3
70
70
18
82
166
100
101
100
22
100
Totals
* As classified, "serious" work was rabbit attack which would kill or conspicuously
malform the plant. "Moderate" work could not be classed as light, but was
hardly serious. "Light" work was inconsequential.
The prickly pears over considerable areas may be consumed in extreme seasons. Ordinarily some individual prickly pears, apparently
as attractive as others (Plate 6, B), are passed by, for what reason we
do not know. The flesh of prickly pear pads is to our taste about as
palatable as spinach.
JACK RABBITS IX ARIZOXA
533
The prickly pear pads are most often eaten from the edge, or, where
the spines are scattered or worn off, they may be attacked on their flat
sides. Entire joints are frequently consumed, and in very dry seasons
the entire plant may be eaten down to the base. Sometimes the cactus
is able to put forth new stems, but not infrequently it is killed.
In the vicinity of Tucson a cholla, Opuntw spinosior (Plate 8) is second choice after the prickly pears, though there is perhaps a question as
to whether the visnaga, Bchnwcactus zinslkenii, may not belong here,
for visnagas are occasionally found heavily eaten by jack rabbits. Once
the armature of an Echinocactus is penetrated, the rabbits eat it with
avidity, often consuming it nearly to the ground surface (Plate 9). The
scattered spines, rabbit tracks on all sides of the cactus, and pellet accumulations clearly indicate the jack rabbit, even if it be not observed in
the act.
In eating cholla or visnaga the hare cuts around the spine patches and
allows them to fall to the ground. With its sensitive nose it feels about
the cactus very carefully, prospecting for a good place to bite in. The
nose is carefully pushed between the spine pads and a hold on the desirable morsel secured. The rabbit often has to pull quite hard to dislodge the piece it is after. The bark may be gnawed to a height of 27
inches. Occasionally one ^ees joints of this cactus stripped (Plate 8, B ) .
Rarely branches are cut off. Rabbits frequently get stuck with cactus
spines, and their movements, a« they nurse or shake their forepaws to
remove the spines, are comical to say the least.
The ultra-spiny chollas, as, for example, Opitntia fulgida, receive
less attention than the others, although on occasion one sees antelope
jack rabbits feeding on this species and even resting beneath it.
The buds and flowers of Echinocereus fendleri are sometimes consumed (Plate 10, A ) . Young sahuaros (Carnegia gigantea) are sometimes eaten near the ground down to the central woody stem.
DISTRIBUTION OF CACTUS
When considerable numbers of rabbits, and the inevitability of their
work on cactus in dry periods, are noted, the probability that the animals
affect the occurrence and distribution of cactus on our ranges may be
readily understood. In an indirect manner the rabbit greatly favors the
cholla although it attacks it somewhat, because pressure is exerted more
heavily on the competitors of cholla (grasses and prickly pear) than
on the cholla itself. Anything that weakens the grasses tends to favor
establishment and growth of new chollas. If this hypothesis holds,
cholla, wherever it is spreading in the range country, is an indicator of
disturbance and really of overgrazing. To the extent that the rabbit
534
TECHNICAL BULLETIN
No. 49
helps cholla, it is somewhat inimical to man's interest, for the cholla is
becoming a pest on considerable areas in southern Arizona. So far as
known jack rabbits do not spread chollas or other cacti directly, as do
cattle and possibh wood rats.
DROUTH AND OVERGRAZING CRITICAL
Two factors are of major importance in relation to jack rabbit work
on cactus and other vegetation.
First, when too many livestock are permitted on an area, attacks by
both stock and rabbits on all palatable vegetation are inevitably more
serious and severe.
A second factor influencing the relation of jack rabbits to vegetation
is the obvious one of drouth. A few weeks at the driest period of the
year may be more significant for the future of the vegetation than all
the rest of the year. Similarly the activities of jack rabbits at the
climax of a long drouth may be more far-reaching than through many
years of less extreme weather conditions. In southern Arizona the
seasons of 1917-1918, 1922-1923, and 1924-1925 were especially dry.
It is recalled that Thornber's cactus planting experiments (Thornber,
1911, pp. 491-493) were much interfered with and some of them wrere
absolute failures because of the work of jack rabbits at dry periods.
In the early years of the Santa Rita Range, i.e., between 1905 and
1910, Griffiths planted a considerable number of prickly pears. These
cacti, while suffering some losses at intervals, were still for the most
part in flourishing condition after 20 years. In the drouth of 19241925, however, all were killed. Cattle had a part in this, of course, but
jack rabbits were probably chiefly responsible.
The influence of jack rabbits on the occurrence and distribution of
cactus, as well as of grass and other plants, is therefore related in a
rather definite and intimate way to the amount of grazing and the severity of the ever-recurring dry seasons.
Where climatic conditions somewhat handicap the prickly pear the
jack rabbit is an important check. It seems obvious, as pointed out by
Griffiths (1928, p. 9) that west of the Pecos River, Texas, the growth
of pricklv pear i^ comparatively slow, owing to the lack of both fertilitv
and moisture. Similar conditions prevail through much of the arid
Southwest In places more favorable to the pear this animal apparently has little influence. It occurs very commonly in southern Texas
— but the prickly pear and mesquite have taken much of the country.
The jack rabbit should not be introduced into Australia, India, or
Africa in the hope that it will control prickly pear!
JACK RABBITS
IN ARIZONA
535
SPINES AS A PROTECTION TO DESERT PLANTS
While spines have been considered to afford protection against animals to the plants of arid lands, our observations indicate there are distinct limits on their protective powers. It is true that spineless cacti
are rarely, if ever, found on the open ranges, but are restricted to well
protected sites on steep canyon walls where cattle cannot, and jack
rabbits do not, ordinarily go, while the extremely spiny cacti, as Opuntia fulgida, and most visnagas are protected by their spiny armature
from attack.
In spite of their spines, however, the prickly pears are regularly attacked and in dry times consumed by rabbits, wood rats, and cattle.
Opuntia spinosior is also attacked, though to a much less extent. Even
the visnaga and the ''jumping" cholla (Opuntia fulgida) are not immune.
Of themselves, spines are evidently insufficient to afford complete protection to the plants of arid lands. The character of the spines, the
kinds and numbers of animals, and especially, the dryness of the seasons, all influence the results. W e derive the impression that the spines
are not so much essential organs produced by natural selection for the
protection of desert plants as they are the structural results of the pressure of certain climatic conditions, especially dryness, on the vegetation, and that such protective influence as they may possess is incidental.
JACK RABBITS AND GRASS
IBPUS
ALLHNI
Among grasses found in stomachs of he pus alleni a r e : Aristida sp.,
Bouteloua, two species, Bragrostis sp., Trichloris meiidocina,
Valota
saccharata, Panicum sp., Bouteloua aristidoides, Cenchrus sp., Sporobohts sp., Briochloa acianinata, Agrostis sp., Chaetochloa sp., Bchinochloa sp., and Chloris sp., or 13 genera and at least 14 species. W e have
no concrete evidence of any jack rabbit eating Heteropogon
contortus,
Andropogon,
or the large Hilarias.
Mesquite grass (Hilaria cenchroides) does not appear in the stomach analyses though the rabbits undoubtedly eat it. There is little doubt that the jack rabbit feeds on
nearly all the species in their succulent stages.
Jack rabbits are hungry animals and their digestive powers are rapid
and efficient. They feed almost continuously, and literally for hours at
a time. Grasses palatable to cattle seem to be equally palatable to jack
rabbits. These hares — at least under present conditions, where the
range is often overgrazed — are possibly harder on the range than the
cattle are, as they can graze more closely than cattle. Jack rabbits
could, but seldom do, penetrate under bushes and crop off the grasses
that cattle cannot reach.
536
TECHNICAL BULLETIN
No 49
There is little question that jack rabbits cut off and waste a good
deal of grass. This grass-cutting habit has been observed by the
authors and by Aldous. In Plot 1A, Santa Rita Range, we often note
large patches of dry grass which have been cut, many stalks left lying,
and almost none standing. The presence, in every instance of cutting,
of the large and unmistakable pellets of jack rabbits indicates that these
animals are in large part responsible.
On April 12, 1923, it was noted that jack rabbits had cut off nearly
all the tall grasses in the afternoon shade of certain of the bushes. Abbey
(1909, p 95) has referred to the habit of Lepus timidus cutting and
clearing away large open spaces to allow them more room to play
LHPUS CALIFORNICUS
Grasses identified in the stomachs of californicus include the following: Agrostis sp, Aristida sp.} Boutehua aristidoides, Bouteloua eriopoda, Bouteloua sp., Trichloris mendocina, Panicum sp., Hilaria sp , Festuca, Eriochloa acwninata, Valota saccharata, Chaetochloa sp , Eragros*is sp., and Sporobolus flexuosus For this lot of stomachs the diagrams show that about a quarter of all food taken was grass Since
fewer stomachs of calif ornicus than of alleni were secured we do not
have an adequate basis for comparison of food habits As pointed out
by Aldous, who has worked principally on calif ornicus, estimating jack
rabbit injury to grass by stomach examinations alone is misleading, for
the grass wasted should be given attention as well as that consumed.
As with the antelope jack, this species bites down many of the tall grass
shoots, eats the lower succulent portion, and leaves the upper 80 percent of the stem lying on the ground. The cut stalks may not be available as food for stock.
The graph (Figure 3), while it indicates the importance of grass in
the diet of the Arizona jack rabbit, suggests that for this species grass
is not so important as for the antelope jack rabbit. This rinding accords
with our observation of the distribution of the two species of jack rabbits. While the antelope jack rabbit is the principal hare on the grassy
bahadas of the Santa Rita and Baboquivari ranges and in similar localities, the Arizona jack rabbit is more common in the semi-desert areas
where grasses are scarce, and weeds and browse more in evidence.
GENERAL EFFECTS
Table 11 shows the possible amounts of the different major items of
vegetation, including grass, mesquite, and miscellaneous vegetation, consumed by jack rabbits, if our estimates as to weight of food consumed
538
TECHNICAL BULLETIN
No. 49
by individuals daily and numbers of the animals present (see p. 559) on
the Santa Rita Range are approximately correct. The figures given do
not afford am indication of the amount of grass cut and left lying
uneaten.
Hensel (unpublished MS, 1919} estimated the average total forage
productivity of the Range at 1,100 pounds per acre per year, one-half
of which was counted as available to stock under conditions that would
not result in overgrazing. At this rate (550 pounds per acre per year),
probabh not excessive for the Range under conservative management,
the amount of production for the entire area would approximate 27,500,000 pounds, or 13,750 tons per year. The calculated amount of
this potential product consumed by jack rabbits, including both grass
and weeds, is 402 tons, or 2.9 percent As estimated by Hensel, forage production on the Range includes chiefly or principally grass. If
the weeds are omitted and only the grass portion of the rabbit's food
is compared with potential grass production on the Range, the amount
eaten by rabbits is reduced to slightly more than 2 percent.
It will be recalled that our determinations (see p. 516) indicate that
on the average 30 individuals of californicus will eat as much valuable
forage as one sheep, and 148 as much as one cow; and that 15 alleni will
eat as much valuable forage as one sheep, and 74 as much as one cow.
When added to conservative grazing by cattle the pressure of jack
rabbit grazing may at times be enough to produce a condition of overgrazing. The heavier the grazing by livestock the more opportunity
there is for jack rabbit grazing to be harmful. Consequently the more
conservatively a pasture is grazed the less serious is the damage by jack
rabbits likely to be.
A long-continued drouth may result in overgrazing by stock and jack
rabbits even when under all ordinary conditions the grazing pressure
would not be too great. These considerations emphasize the necessity
for stocking the ranges according to the poor seasons, rather than the
best season or even the average season. Forsling (1924, p. 5), directly
advocates limiting breeding cattle to range capacity in poor years.
Under all but the most conservative stocking with cattle the tendency
of grazing by jack rabbits will be to accentuate overgrazing, to eliminate the more palatable grasses and favor their replacement by somewhat less desirable species and by weeds.
Matthams (1921, pp. 234-235) points out that in Australia rabbits
assist the weeds to survive and displace the nutritious grasses. He
says areas about rabbit warrens are often seen upon which weeds are
abundant, and that many instances can be cited where, when rabbits
JACK RABBITS
IN ARIZONA
539
and stock have been excluded from such areas, the natural grasses have
in a great measure displaced the noxious weeds. " W h e r e the natural
grasses grow more quickly and luxuriantly than the weeds, the latter
are handicapped in their struggle to survive, and where the growth of
pasture is retarded and the constitution of the plant weakened by rabbits the weeds are assisted to a corresponding degree."
JACK RABBITS AND W E E D S
The variety, but nor a complete list, of weeds consumed by jack rabbits is indicated by the stomach anal>ses. A small amount of additional
evidence has been derived from direct observation. Thus the rare Carlozvrightia UnearifoUa, though never identified in rabbit stomachs, is
nevertheless so heavily grazed by rabbits that its survival is doubtful in
areas where the animals are numerous. On the Jornada Range, snakeweed (Gutierrema juncea) is clipped and perhaps eaten to a slight extent. Bphedra trifurca is also eaten on the Jornada, and occasionally
the plants are stripped of all foliage in reach. Petals of Psilostrophe
tagetinae have been found in rabbit stomachs, and Ilriogonitm
annuum
is known to be eaten. Us^hscholtzia mesicana is freely consumed whenever it is available. W h e n the showy Kallstroemia grandiflora appears
the rabbits eat it to a certain extent also. Rarely jack rabbits chew
on burroweed (Isocoma coronopifolia),
a common and very troublesome poison plant on the Santa Rita Range.
T h e animals are known to feed extensively on fllaree in some places.
In other localities jack rabbits are wTell known to eat a variety of weeds.
T w o specimens taken near Beswick, California, by Gaut and Ferry,
September, 1905, had masticated a mass of the yellow tops and dark
frosted lower leaves of rabbit brush (Chrysothamnus
occidentalis).
Bailey (October IS, 1888) found rabbits eating seeds and probably
leaves of pigweed (Chenopodium)
near Ogden, Utah. Near Voltage,
Oregon, in the summer of 1920, the same observer recorded rabbits
feeding on a variety of vegetation including tules, salt grass, buftcbgrass, three or more kinds of pigweed, greasebrush, Grayia sp., Tetradymia sp., and Chrysothamnus sp.
Apparently rabbits can make use of many different species of weeds,
but only do so, ordinarily, when succulent grass is lacking. T h e most
important effects of jack rabbits on weeds, ast on browse, are probably
indirect. Though the animals work directly on weeds their destruction of grass must relieve the seedling weeds of much competition.
There is littld question that jack rabbit work, at least under conditions
of overgrazing, is on the whole favorable to weed growth (Plate 1 2 ) .
JACK RABBITS IX ARIZOXA
541
On the basis of extensive observations of vegetation in the arid Southwest as related to the influences surrounding it, Cooperrider is of the
opinion that the order of rabbit preference for plants, when available, is
annuals and then perennials followed by grass.
This observation accords with our own findings that jack rabbits
are more abundant in areas where weeds are common than in those
where climax stands of grass occur. It is entirely possible that our
stomach analyses are not really numerous enough to show true conditions, aside from the difficulty of identifying the small succulent annuals
m the stomachs. It may well be that we have over-emphasized the
rabbit's liking for grass.
JACK RABBITS AXD CROPS
The jack rabbit is extremely fond of alfalfa, young cotton plants,
young grape vines, lawn grasses, and ornamentals. This phase of the
food habits of the animal will be more fully treated under economic
relations.
ANIMAL FOOD
Goldman gives reports by natives in the vicinity of Camargo, Tamaulipas, January 4-29, 1902, that Lepus californicus merrimni in that vicinity sometimes fed on the carcasses of dead horses. An American resident assured him that in Lafayette County, Texas, they were known
as horse rabbits on account of this habit.
Insect remains occur infrequently in rabbit stomachs. Only 3 out
of 61 stomachs of L. californicus showed insect or other Arthropod
material, while only 20 of 179 stomachs of L. alleni contained traces of
Arthropods. Apparently all insect material found in the stomachs was
of an accidental character.
MINERAL ELEMENTS
While no notable jack rabbit concentration has been observed about
salt put out for cattle, our observations and those of Aldous indicate
that salt or some other mineral element is frequently sought.
At the United States Rabbit Experiment Station, Fontana, California,
a spool of salt and sulfur is regularly hung in the cages in which domestic rabbits are kept. The rabbits lick or even eat this material. Rabbits have been found to consume more food which has been salted than
food that has not. A rabbit consumes more salt when molting than
at other times. It is likely that wild hares must also secure a certain
amount of mineral matter for the maintenance of their health.
542
TECHNICAL BULLETIN
No. 49
Elliot and Crichton (1926) have shown that high mineral content of
pasture grass is associated with, high nutritive value for livestock Not
only that, but these authors and also Godden (1926) have pointed out
that deficiencies in mineral elements in pasture grasses are associated
with specific nutritional diseases.
For several years we have observed a rabbit "lick" on the southwest
slope of one of the red hills north of Plot 1A on the Santa Rita Range
(Plate 10, C). Rabbits, mostly alleni, are numerous in this neighborhood. The animals have dug or bitten into the dark red earth, and
fecal pellets are abundant. Analysis of the soil of this "lick" has not
shown any salt or saline constituents. Many rabbit pellets found nearby
are so coated with red earth as to resemble little red balls of mud.
Breaking the pellet shows that the red earth is a surface coating over
the remains of vegetation normally present. Rabbit pellets, similarly
coated with red earth, have been observed west of Benson, Arizona,
and southwest of Vail, Arizona. Jack rabbits have recently (1932) dug
holes a foot deep in one of the corrals on the Santa Rita Range and
have several times been observed eating the earth from the steep sides
of these excavations That salt blocks had lain at these places seemed
an obvious conclusion, but analysis of the soil showed only a slight trace
of salt; less, in fact, than is contained in the well water supplying the
city of Tucson
Gravel or sand was recorded in 26 out of 61 stomachs of calif ornicus
and in 97 out of 179 of alleni. The material was found in stomachs
collected from April to October. In some of the stomachs the records
were not complete, so that more stomachs rather than fewer actually
contained this material.
FEEDING
The jack rabbit feeds at night, before and after sunrise, and for several hours of the morning, say up to 8 or 10 o'clock. Toward evening
they begin to feed at from 4 to 6 o'clock, depending on the time of year.
On cloudy days, rarely otherwise, they feed during midday hours. Jack
rabbit stomachs examined were never empty, no matter what time they
were taken.
The ratio of the weight of stomach contents of the antelope jack rabbit to weight of animal is low, ranging from 07 percent to 3.5 percent,
and averaging 1.7 percent.
Food seems to traverse the alimentary tract very rapidly. When a
small rabbit in our cages ate Bouteloua aristidoides, dry, its feces were
larger and light brown, like most of the pellets observed on the range,
JACK RABBITS
IN ARIZONA
543
and averaged 7 to 9 mm. in diameter. W h e n feeding on green alfalfa
the feces were small, almost black, and averaged 6 to 7 mm. in diameter. After continuous feeding with alfalfa, the rabbit was fed Bouteloua at 6-7 p m .
"Bouteloua"
feces were numerous twelve hours
later.
ENEMIES
To what extent can the natural enemies of jack rabbits be relied on
to hold the animals in check ? We shall now discuss these enemies and
their possibilities.
COYOTE
GENERAL RELATIONS
Coyotes, the most widely distributed of the flesh-eaters in jack rabbit
territory, have long been recognized as enemies of these ofttimes troublesome animals. The first adequate discussion of the interrelations of
coyotes and rabbits was given by Palmer (1897, p. 45), who pointed out
that the coyote is a most effective rabbit destroyer and accomplishes
more good in this way than it usually receives credit for. He also
mentions the California coyote bounty law, in effect from March 31,
1891 to September 30, 1892. Following the destruction of scores of
thousands of coyotes, rabbit increase was so great that shortly, in at
least one county (San Bernardino), a bounty of 20 cents apiece was
offered on rabbits.
In 1905 (p. 177) Bailey pointed out that on the one hand the coyote
kills many sheep and a few goats, some poultry and considerable game,
while on the other, the bulk of its food the year around consists of rabbits, prairie dogs, ground squirrels, gophers, wood rats, mice, and small
rodents.
Jewett in 1910 asserted that Lepus californicus wallawalla in the
vicinity of Vale, Oregon, formed the main food supply of the coyote.
Warren (1910, pp. 248-249) has called attention to the fact that
coyotes kill many rodents, cottontails, and jack rabbits in Colorado.
Cary's observations in the same State (1911, p. 73) offer further
evidence of a similar character.
Baker, Korstian, and Fetherolf (1921, p. 310) report that with the
destruction of a large number of coyotes, the principal enemy of rabbits in the Wasatch Mountains, Utah, there has been a considerable
increase in the number of rabbits and a corresponding increase in damage to conifers. This is an interesting illustration of the fact that predatory mammals quite frequently are friends of the forest.
544
TECHNICAL BULLETIN
No. 49
Sampson (1928, p. 350) says, "Rabbits, prairie dogs, ground squirrels, gophers, field mice, and chipmunks are staple articles of the coyote
diet. . . . Organized warfare against the coyote has doubtless resulted
in appreciably increasing the rodent population in some localities. However, this disturbance in the balance of nature, as it has been termed,
favoring the rodents, is not very serious, as effective methods are also
available for holding in check the rodent population." Unfortunately
no completely satisfactory method of rabbit control has been devised
for the warmer southern part of the western range country, where
obviously, the difficulty of baiting rabbits is much greater than in the
cold northern regions where the snows of winter tend to concentrate
the rabbits and make them desperately hungry.
Ligon (1927, p. 108) notes that the killing of coyotes, badgers, and
large prairie-dwelling hawks has had a tendency to increase the numbers of the black-tailed jack rabbit in New Mexico.
Will and Emmet Isaacks, cattlemen of Las Graces, New Mexico, and
other ranchers in that vicinity, believe the coyote is an important check
on jack rabbits. The rabbits are a real problem, they say, while under
present conditions the coyotes do no harm on stock ranches. Forest
Service officials and stockmen on the Jornada Range, are unanimously
of the opinion that the coyote is a check on the increase of jack rabbits.
At present (1930) coyotes are extremely abundant and rabbits noticeably less numerous than usual. Professor J. L. Lantow, Animal Husbandman of the New Mexico College of Agriculture and Mechanic
Arts, is "positive" the coyote is an effective check on jack rabbits.
R. L. Moore, manager of the 504,000 acre Waggoner Ranch at Vernon, Texas, believes that coyotes are an important check on rabbits and
prairie dogs. Mr. Moore allows no trapping on this extensive property.
Supervisor Rex King of the Crook National Forest, Arizona, says
he has noticed in localities which are the natural habitats of jack rabbits
that a drive on coyotes is followed by an increase in rabbits.
A. M. Philipson, U. S. Indian Service, reports that coyotes keep down
jack rabbits on the Papago Indian Reservation, southern Arizona.
RABBITS IN COYOTE STOMACHS
Of 680 stomachs of coyotes taken in the State of Washington (19171919) on which rough records of stomach contents were kept by State
and Biological Survey hunters, 85 stomachs, or \2l/2 percent, contained
rabbit (probably including principally L. c. wallawalla, with some L.
iownsendii townsendii and Sylvilagus nuttallii nuttallii). Tables given
by Henderson (1930, pp. 345, 348) show that out of 36,989 coyote stom-
JACK RABBITS
IX ARIZOXA
545
achs examined by Biological Survey hunters from 1910 to 1923, 7,029 or
21 percent contained "rabbit"; and of 59,170 stomachs examined from
1924 to 1928, 12,141 or 20 percent contained "rabbit."
SEASONAL, CYCLICAL, AND LOCAL ASPECTS
The relation of the jack rabbit to the co\ote population is subject to
marked variation. When rabbits are abundant, co\otes ma\ secure
many, when scarce, few. An estimate of the significance of the co\ote
as a jack rabbit enemy based on stomach examinations during a season
of either abnormally large or small numbers of rabbits might therefore
be misleading. Under anything like natural conditions coyote-rabbit
relations are automatic in character; but the rabbit probabh has more
to do with coyote numbers than the coyote does with rabbit numbers.
Trappers in the San Angelo, Texas, region reported to Bailey that
the rabbit was rarely found in coyote stomachs in 1918 while the previous year it was generally found. Dixon (1925, p. 45) found that
coyotes in northern California showed a high percentage of game and
domestic stock eaten, while stomachs from the southern part of the
State showed ground squirrels and jack rabbits predominating.
Henderson (1930, p. 338) refers to studies of the coyote in Xevada
in winter, which showed that rabbits were its principal food. With
disappearance of the snow, however, the coyote had greater difficulty
in catching rabbits, and turned to herds of domestic sheep.
CHECK AND BALANCE RELATIONS
"An unusual increase of jack rabbits in any region is always followed by a corresponding influx of coyotes," says Bailey (1905, p. 177),
"which probably accounts in part for the often-observed fact that in
the years following their maximum abundance jack rabbits are unusually scarce."
Nelson (1918, p. 424) after referring to efforts of the Federal Government to suppress coyotes, says, "The complete destruction of coyotes
would, no doubt, upset the balance of nature in favor of rabbits, prairie
dogs, and other harmful rodents, and thus result in a very serious increase in the destruction of crops."
Evidence on increase of jack rabbits following coyote eradication is
conflicting. Most of it is uncritical and the best leaves much to be
desired. There are reports, particularly from Texas and Utah, that
rabbits and rodents have not increased following eradication of coyotes
and other flesh-eaters. There is so much competent testimony, however,
that jack rabbits often do increase following coyote eradication that it
cannot be lightly dismissed. Of course other factors entirely aside
546
TECHNICAL BULLETIN
No. 49
from predators, as favorable or unfavorable climatic conditions, or presence or absence of disease (see p. 553) may play a part in the observed
variation in numbers of jack rabbits.
There is a feeling on the part of many officials directly concerned
with rodent control, and also among some stockmen, that the activities
of coyotes and other carnivores in controlling jack rabbits and rodents
are negligible. It is felt by the writers, however, that the flesh-eaters
undoubtedly help to regulate jack rabbit numbers. We agree with Gilchrist that while "A few individual coyotes will kill calves, as a general
thing the presence of coyotes on a cow range infested with jack rabbits
or kangaroo rats is to be encouraged. The wholesale poisoning of
emotes and bobcats on cow ranges in the jack rabbit or kangaroo rat
country is to be avoided." (Mimeographed news letter to hunters, Arizona, March 10, 1930.)
BOBCAT
Rabbits constitute one of the principal items in the diet of the bobcat.
One of these animals shot on the Santa Rita Range had its stomach completely filled with rabbit remains.
Bailey (1905, p. 171) writing of Lynx baileyi in Presidio County,
Texas, refers to the ranchmen's complaints of some poultry being killed,
and still worse, a few sheep. It also takes a few quail and other birds.
But there is an even larger sum on the credit side of the account. For
example, bobcat feasts in the rocky corners of the cliffs usually disclosed a great preponderance of rabbits and wood rats. Long-continued field studies of bobcats in Texas convinced Bailey that the benefits
conferred by the animal in consuming not only rabbits but rodents of
other kinds outweighed damage done.
The testimony of other observers is nearly unanimous to the effect
that the bobcat preys consistently on rabbits. Thus Warren (1910, p.
254) says that in Colorado bobcats feed on rabbits, wood rats, mice,
and birds. Cary (1911, pp. 167-168) writing from the same State,
says that bobcats prey much on rabbits and other small mammals. Locally, he says, they are probably to be considered useful animals although
they commit serious depredations to poultry and sheep.
SNAKES
In the mesquite country on Ash Flat in the Graham Mountains, Arizona, May 30, 1914, E. G. Holt found a rattlesnake making a meal of
several very young rabbits. Seton (1929, p. 752) reports the bullsnake and the rattler as important enemies of the jack rabbits.
JACK RABBITS IX ARIZOXA
547
Culley once killed a large rattler on the Santa Rita Range in the act
of swallowing a young jack rabbit as large as a cottontail. When found
the snake had the rabbit all down but the hind feet.
On May 1, 1931, O. N. Arlington of Tucson reported that he collected a rattlesnake (Crotalus atrox) measuring 42 inches without the
rattles, and with a gross weight of 2 pounds, 13 ounces. On dissection two jack rabbits were found in the snake's stomach, a small baby
jack and a larger jack. The snake's stomach was 23$4 inches long. The
smaller animal occupied 5J/2 to 6 inches of the space and the other
approximately 18 inches. Together the jack rabbits weighed 1 pound,
3 ounces; snake carcass, 1 pound, 10 ounces.
BIRDS
Almost all of the larger birds of prey feed on jack rabbits. Palmer
(1897, p. 44) and Lantz (1908, p. 336) have published detailed lists
of the bird enemies of rabbits.
That the golden eagle, great horned owl, western red-tail, ferruginous
rough-leg, and bald eagle feed extensively on rabbits is attested by stomachs and pellets examined by the Biological Survey, and bones found on
or near nests. Sometimes an unusual accumulation of material was discovered at predator nests. In the Davis Mountains, Texas, Bailey found
remains of at least 100 cottontails, together with a few young jack rabbits, in the debris about a horned owl's nest. It is not improbable that
young jack rabbits are more frequently taken than the older ones. One
observer near Albuquerque, New Mexico, saw a ferruginous rough-leg
kill a jack rabbit.
An increase in jack rabbits following killing of their natural enemies,
the hawks, is mentioned by Ligon. He reports that in the Pecos Valley, New Mexico, in 1918 there seemed to be few natural enemies of
rabbits, which were extremely abundant, so numerous in fact, that they
were killed and shipped to market as a commercial proposition. Ligon
(1927, pp. 58-59) makes a strong plea for the hawks and owls, especially the red-tail, rough-leg, and Swainson, as destroyers of rabbits,
prairie dogs, and other injurious rodents.
Golden eagles have been found feeding on antelope jack rabbits on
the Santa Rita Range. We have examined many nests of western redtails and western horned owls on the Santa Rita Range but hav$ failed
to find any jack rabbit remains, although parts of cottontails and smaller
rodents were plentiful. Jack rabbit bones together with fragments of
cottontails, wood rats, meadow mice, and pocket gophers were found in
owl castings under a large pine tree near Flagstaff, Arizona.
548
TECHNICAL BULLETIN
No. 49
MISCELLANEOUS
Among- other enemies of jack rabbits in the Southwest are gray foxes
(Bailey, 1905, p. 181; Warren, 1910, p. 236); badgers (Palmer, 1897,
p. 44); man, especially the aborigines and some of the Mexican population, as well as farmers, irresponsible shooters, and sometimes hunters
for the market; the automobile, forest fires, drouth, hail, and extremely
cold weather.
CONCLUDING REMARKS ON ENEMIES
The extent to which natural enemies of jack rabbits can be relied upon
to hold these animals in check is an ever-recurring and fertile subject
of discussion. Admittedly the extent to which natural enemies prey
upon them, and the practicability of relying upon predators for satisfactory control of jack rabbit abundance, are dependent upon local conditions, including the type of crop and livestock production prevailing
in the region.
Under present conditions in Arizona the predators which feed upon
jack rabbits to an extent that renders them a factor which should have
consideration in a program of wild-life administration would include
the coyote, bobcat, gray fox, the bull snake, and rattlers, some of
the larger hawks and owls, and the eagles. The problems involved in
control of jack rabbit populations by natural enemies are exceedingly
intricate and their solution is rendered particularly difficult because of
the well-known tendency of these animals to fluctuate greatly in numbers, evidently due to the operation of a variety of causes which up
to the present time have not been subjected to adequate critical investigation. Interpretations offered of observations made in many localities and by interested individuals have varied widely in conclusions
reached. Commonly conclusions announced are clearly modified by the
viewpoint of the individual, the extent to which there has been opportunity for long-time and comprehensive accumulation of facts and a
disposition to weigh carefully the various factors that may have been
operative. Manifestly snap judgment cannot be relied upon to provide
a satisfactory solution of these varied and important relationships. Based
on their field studies the authors of the present paper would emphasize
the need for intensive study of this problem in order that comprehensive data may be accumulated and careful evaluation made of the importance of the various factors involved as a basis for a sound wording
program in future handling of lands populated by jack rabbits. Fortunately the Biological Survey and its cooperators are now engaged in such
a study from which it is hoped that information may be secured and
conclusions reached which will prove helpful in dealing with this important problem.
JACK RABBITS
IN ARIZ OX A
54Q
PARASITES AND DISEASES
ARTHROPODS
Arthropod parasites of jack rabbits include flies, fleas, possibly sucking lice, and ticks.
The largest and most conspicuous of the insect parasites are the dipterous larvae commonly known as "warbles," related to the ox warble
or grub (Hypodernia) which lives in the backs of cattle. Rabbit warbles belong to the genus Cuterebra* (family Oestridae). They are
large, dark brown or black, squirming grubs which live in mucoid cysts
in the subcutaneous connective tissues. The surface of the warble is
hard, spiny, and feels like a rasp. Since each, while still resident beneath the skin of the jack rabbit, becomes as large as the last joint of a
man's middle finger, one may well imagine the resultant irritation. From
one to several may be present in the throat or rump of a single animal.
In an extreme case no less than 13 large and 3 young warbles were
found in the throat of one antelope jack rabbit. Some years, nearly
all of the rabbits are infested; in others, warbles are scarce. A sudden
reduction in numbers of these parasites took place in 1927-1928; nor
has the infestation appreciably increased up to date (February, 1933).
Since the life history, especially the mode of infestation, of Cutercbra,
is unknown, some facts which may be significant are worth recording.
The adult insects are large, black flies which wottld be conspicuous about
the jack rabbits if they commonly hovered about them for oviposition;
but we have never seen one about its host. Only two specimens of the
adult have ever been taken in the field by members of the Department
of Entomology of the University of Arizona, and these were neither on
nor near jack rabbits.
There is no apparent seasonal periodicity in the occurrence of younger
and older larvae. Large, apparently mature wrarbles are found at any
time of year, and young grubs may occur at the same time in an individual host. On two occasions young jack rabbits have been found infested
with nearly mature warbles, one of these rabbits weighing only about
3 pounds, the other just above 4 pounds. Since the adult flies probably
appear at a definite season, it is unlikely that they oviposit directly on
the host; for if they did so there would be an obvious periodicity in the
larval stages. The eggs should be conspicuous if placed on the hair of
the host, but in handling hundreds of rabbits the eggs have never been
* Cuterebra prmceps and C. americana have been determined for us by Mr. F. C.
Bishopp, United States Bureau of Entomology.
550
TECHNICAL BULLETIN
No. 49
found. It has been suggested that the eggs may be placed on vegetation, whence they are ingested by the host animals; a suggestion which
our observations support. If this be the method, the actual infestation
might occur at any time of year or at several successive times in the
same year for a single host.
Only 31 percent of the antelope jack rabbits examined since 1928
have shown Cuterebra infestation. Of the infestations recorded, 60 percent were in the throat, and 40 percent in the rump. In the Arizona jack
rabbit, in the same period, the infestation has been SO percent, all in the
rump. Prior to 1928 throat warbles were undoubtedly more abundant
and occurred in californicus as well as in allenL Whether the throat
and rump are infested by different species of Cuterebra has not been
determined. Bailey has observed Cuterebra larvae in the eyes of jack
rabbits in Oregon.
Fleas, though reported by some observers to be abundant on jack
rabbits, are not common in southern Arizona. In fact, on a number
of specimens of both species it was impossible to find fleas. On many
others but few were found. For calif ornicus other observers have
noted heavier infestations. On the Santa Rita Range in January, 1921,
Bailey noted that fleas were found abundantly on jack rabbits, which
at times fairly swarmed with them. We have never been able to
confirm this. Aldous, in November, 1929, examined 45 jack rabbits
on the Jornada Range, finding all infested with fleas; and in January,
1930, he recorded 38 from Mesa, Arizona, as 100 percent infested. One
species of flea (Hoplopsyllus affinis) occurs on both jack rabbits, and
the cat flea (Ctenacephalides felis) has also been taken from californicus.*
Although careful search has been made, we have found neither sucking lice (Anoplura) nor biting lice (Mallophaga) on jack rabbits. This
is not strange, since the literature fails to reveal a single record of occurrence of a biting louse on any species of North American rabbit; and
only the following records of Anoplura from wild rabbits in the West.
Kellogg and Ferris (1915, p. 28) and Ferris (1916, p. 102) have reported sucking lice (Haemodipsus ventricosus) from L. califorwicus in
Sonoma and Humboldt counties, California, and from L. c. deserticola,
Ehrenberg, Arizona. Francis (1922, p. 23) has recorded the same parasite from jack rabbits in Utah.
The jack rabbits of southern Arizona are commonly infested with
ticks. The seasonal distribution of young and adult ticks is so distinct
that they were supposed, prior to specific identification, to be different
51
Determinations by F. C. Bishopp
JACK RABBITS IN ARIZONA
551
species. All have been identified, however, as Dennacenior parumaperius
marginatus
The large, engorged adults are found in great numbers
on the ears and around the eyes of jack rabbits during the summer
months, appearing in May and disappearing in September, or at the
latest, October. During June and July nearly every jack rabbit of both
species is infested. In late autumn and winter quantities of the young
or seed ticks, of the above species are found on the ears and eyes of
both jack rabbits, first appearing in October and becoming most abundant in November, December, and January. While an individual host
animal may carry a large number of these young ticks, the percentage
of jack rabbits infested appears to be less than in summer.
TAPEWORMS AND NEMATODES
The most conspicuous of several "worms" which parasitize the jack
rabbits is a species of tapeworm (Multiceps sp.) which occurs within
the rabbit in the "bladder worm" or cysticercus stage, i.e, the rabbit is
the secondary or intermediate host. The coyote is probably the primary
host. The watery cysts of this parasite may be found at any time of
year, occurring in an estimated 10 to 20 percent of the hosts, the degree
of infestation showing some variation in different years. These cysts
may occur in almost any part of the body. In the muscles they vary
from the size of a sparrow egg to that of a man's fist. When of large
size they may be evident as distinct swellings on the living animal ( Plate
11, A ) . In two or three instances a bulk of cyst material estimated at
nearly a quart occupied the body cavity of the host (Plate 11, B ) . Several cysts may occur in a single badly infested individual. Two specimens have been taken in which a cyst the size of a small hen's egg was
so placed between the jaw muscles on the side of the head as to force
the lower jaw to one side, causing the incisor teeth to wear off in a
diagonal slant, and distorting the molars so as to render eating difficult
or nearly impossible. Both specimens were poor and probably not far
from starvation. In one of these the stomach was full of coarse, un~
chewed grass and weeds.
W e have but a single record of a mature tapeworm occurring in the
jack rabbit. Nichol took a specimen of Raillietina sp. from the small
intestine of Lepus alleni.
Small nematodes of two species have been taken from the alimentary
canal of the jack rabbit. One of these, Nematodirus sp., is found in the
intestine; the other, Dermatoxys veligera* is rather common in the
* All determinations of nematodes and tapeworms by the Bureau of Animal Tndtistry, U. S. Department of Agriculture
JACK RABBITS IN ARIZOXA
5o3
coecum. We have observed no instances in which either of these appeared to be of great importance to the host.
In spite of the high incidence of parasitism among our jack rabbits
there is little evidence that parasites have affected the numbers of the
animals in southern Arizona during the past 10 or 12 \ears. It is reasonable to suppose, however, that in extreme cases weakening of the
host occurs, leading perhaps to the capture of the jack rabbit by a coyote
or other predator.
Marked fluctuations in numbers of jack rabbits do not occur in the
southern Arizona region, nor do we have the extremes of parasitism or
of disease that are so conspicuous in some other places. As might be
expected, extreme infestation with parasites, and serious outbreaks of
disease, appear to be definitely correlated with excess population of jack
rabbits. Thus, Bailey, in eastern Oregon, in the early autumn of 1920,
sketched the following vivid account of conditions among the jack rabbits there.
"At the present time, August and September, the rabbits are dying
off rapidly from various diseases. Almost as many dead as alive are
seen and many sick individuals are so far gone that they are stupid and
may be picked up by the ears without effort to escape. Many were
seen actually dying and watched as they made their last kick, then examined for symptoms.
"Many were heavily infested with Cuterehra and some had both eyes
destroyed or so crowded with these parasites as to be unable to see. I
watched a Cuterebra larva crawl out of the corner of the eye of one rabbit as he sat under a sagebrush and the other side of his head was puffed
out by several more. Some had bunches over their backs and sides until
they were misshapen with them, but T do not know that these alone
caused death.
"Some of the rabbits have large bunches of transparent fluid with
white specks in it, the tapeworm larval cysts, under the skin and in
the body cavities. In heavily infested individuals these were like bunches
of white grapes among the intestines, in the thoracic cavity and in the
liver and kidneys, apparently enough to kill the rabbit.
"In other rabbits watched in their hst death struggles the symptoms
were different and apparently not due to parasites. One had a greatly
enlarged heart, filled up with white, hard tissue, congested and spotty
liver [this lesion indicates tularernia], congested lungs with many hemorrhagic spots, enlarged and softened kidneys, and dark red muscle. After
the first good rain the rabbits scattered out over the higher ground and
apparently the mortality decreased."
S54
TECHNICAL BULLETIN
No. 49
TULAREMIA AND OTHER DISEASES
Considering the number of jack rabbits which we have examined more
or less carefully the percentage of obviously diseased animals found is
surprisingly small
Perhaps the most important disease of jack rabbits, certainly the one
of greatest present interest, is tularemia or "rabbit fever/' which is infectious, plague-like, and frequently fatal to rodents and rabbits. It is
readily transferred to man by ticks and blood-sucking insects, or by
personal contact with diseased rabbits. In man it is a debilitating, disabling, and sometimes fatal malady, with a death rate of about 4 percent.
Generally recognized m man as an important disease for scarcely
more than a decade (Francis, 1922) tularemia has already been reported
in all but three of our states. Although we have not personally encountered any case in rabbits, Hull (1930, p. 210) records two cases
of tularemia in man in Arizona.
Obviously the incidence of the disease is less in this region than in
some others. Nevertheless, since rabbits and hares constitute the great
reservoir of infection in the United States, it seems desirable to sound
here a note of warning.
If an epizootic disease breaks out among the rabbits leave them severely alone. Beware always of poor, emaciated, weak, or obviously sick
rabbits of any species. If such be killed, the carcass should be burned,
buried, or similarly destroyed without handling. Rubber gloves should
be used in dressing rabbits if the presence of tularemia is suspected in
the locality. The liver and spleen of a rabbit infected with tularemia
show small white spots — foci of necrosis, or decay, affording what is
perhaps the best evidence of the disease. If an apparently healthy rabbit being dressed or dissected shows evidence of disease at once discard
and destroy the specimen and cleanse the hands as thoroughly as possible, using antiseptic if available. The germ of tularemia can infect a
human through the unbroken skin. In any case, however healthy the
animal may appear, if it is to be eaten it should be thoroughly cooked as
a precautionary measure. Even an infected animal is made safe for
food by heating sufficiently to cook the flesh clear to the bone. Take
no chances on eating rabbit meat "rare." Infection most frequently
occurs from direct contact with rabbits. Thus, of S40 human cases listed
by Hull (1930, p. 218) 453 had dressed or dissected rabbits. Most of
the others had been insect or tick bitten. Ticks and deer flies caused
more infections than other insects known to be capable of transmitting
the disease*
JACK RABBITS
IX ARIZONA
555
O u r records of diseased rabbits in Arizona show onh a few sporadic
occurrences. A californicus female had two large tumors in the vicinity of the shoulders. One was under the skin, with no external opening,
the other was exuding pus, A male alleni had a large spherical tumor
1 inch in diameter in the spleen. Aldous in 1929 examined 45 cahfonucus on the Jornada Range and recorded 2 w ith "pus boils" and 2 with
pylephlebitis (inflammation of the portal vein) A number of cases of
infections or ulcer-like sores have been noted on the genital organs of
both male and female alleni These sores were immediately around the
genital openings, and produced a swollen vulva in the female and swollen
prepuce in the male. Presumably such infections would be transferable
by coitus.
Pus infections of the cavities from which Cuterebra grubs have issued
are common but by no means universal.
Henshaw and Birdseye (1911, p. 20) pointed out that in the Bitter
Root Valley, Montana, several kinds of rabbits, including Lepus bairdi,
Lepus campestris and Sylvilagus nutialhi, carry the ticks which transmit
Rocky Mountain spotted fever.
NUMBERS
FLUCTUATIONS
Marked fluctuations in rabbit numbers, especially in Canada, are well
known. Preble (1908), Nelson (1918), Hewitt (1921), Soper (1921),
Elton (1927), and others have given strong evidence of cyclic fluctuation in northern climates.
From a position of skepticism as to the marked differences in fluctuations in animal numbers in the north and south we have been forced to
conclude that cycles are much harder to trace in the milder climates.
Studies of the jack rabbits of southern Arizona have not revealed
strongly marked fluctuations. This is not saying, however, that lesser
fluctuations do not exist. So far, our counting methods are not refined
enough to disclose minor variations in numbers
Regarding true causes of jack rabbit fluctuations we are still very
much in the dark. The classification of causes of cycles made at the
Matamek cycle conference calls to mind the vagaries and mysteries cited
by the peoples of pre-scientific eras in their flounderings after satisfactory explanations of the insistent natural phenomena all about them.
Many of the causes cited are simply suggestions wihch serve as a cloak
for jgnorance.
556
TBCHKICAl
BULLETIN
No, 49
JACK RABBIT COUNTS
The determination of the numbers of jack rabbits has been one of
the most puzzling and troublesome of problems in this study. Yet, since
knowledge of numbers is essential if estimates of ecologic or economic
status are to mean much in a quantitative way, we have tried several
methods and finally arrived at reasonably satisfactory results.
Something, but unfortunately not much, has been learned by tallying
up the numbers on definite areas as recorded in connection with rabbit
drives.
Jack rabbit censuses by automobile have afforded somewhat better
information.
The best counts of all are those in course of which rabbits and cows
seen were carefully recorded and their ratio on a particular area determined.
Iyigon in 1918 reported that the Pecos Valley, New Mexico, from Fort
Sumner southward for some 160 miles into Texas, was perhaps worse
infested by jack rabbits and cottontails than any other part of the
Southwest. He estimated that rabbits averaged 400 to the square mile
(0.62 per acre) over several hundred square miles of the valley. But
near Carlsbad Cave in the same valley in 1924 Bailey saw so few jack
rabbits that he judged their total numbers would not average more than
three per square mile (0.0047 per acre).
In 1929, Aldous poisoned 101 rabbits on 14J4 acres on the Jornada
Range, 61 cottontails and 40 jack rabbits (2.7 jack rabbits per acre).
Between 1923 and 1927, principally on the Santa Rita Range, we
made more than 50 jack rabbit counts, mostly at times of year when
visibility was best, and usually from an automobile moving at 10 to 15
miles per hour. The counts thus made covered a lineal distance of 238.4
miles, but the time of day was not recorded for all. Assuming that we
had under observation a strip 500 feet wide, the area embraced was
approximately 14,448 acres, on which were recorded 767 rabbits, (34
per section, or 0.053 per acre). At this rate, there would be 2,618 jack
rabbits on the 77 square miles of the Range.
We are certain, however, that this is an underestimate. One never
sees all the rabbits in a 500-foot strip, because of variable attention of
the observer, and low visibility of the rabbits, due to their immobility
and to protective vegetation.
The most satisfactory of these estimates was that made by counting
the rabbits at the time of day when they were visible in greatest numbers. On this basis (90 jack rabbits s&tn before 6 a.m. and after 6 p.m.,
JACK RABBITS IK ARIZONA
557
on a SOO-foot strip 179 miles long) there were 53 jack rabbits per section (0.083 per acre), or 4,088 on the entire Range. Even this estimate is quite likely below the actual numbers.
Table 12 includes all counts in which time of day was recorded. In
all these counts made before 6 a.m. and after 6 p.m., five jack rabbits
were seen to the mile; in all counts before 8 a.m., and after 4 p.m., 4.3
per mile; in all counts between 8 a.m. and 4 p.m., 2.3 per mile; while
between 10 a.m. and 2 p.m. but 1.5 were noted per mile.
Another method of counting jack rabbits was tested which in our opinion gave the best results obtained. Both jack rabbits and cattle were
counted and a ratio established. The approximate number of cattle on
the Range being known, an estimate of the total jack rabbit population
was made.
No. of
counts
TABLE 12.—JACK RABBIT COUNTS O N T H E SANTA RITA R A N G E
(1923-1927).
Time of day
Total
jack
rabbits
Total
of
miles
5
Before 6 a.m., and after 6 p.m
90
17.9
5.0
24
Before 8 a.m. and after 4 p.m
360
82.1
4.3
19
Between 8 a.m. and 4 p.m
149
63.8
2.3
5
Between 10 a.m. and 2 p.m
24
16.3
1.5
Jack rabbits
per mile
Jack
rabbits
per cow
Jack
rabbits
per sec.
Jack
rabbits
per A.
2358
207
68
3.04
5.3
54
.085
Mesa
37.6
2280
535
133
4.02
14.2
149
.233
Foothill
8.6
527
50
20
2.50
53
60
.095
Count 14*
6.0
364
30
25
1.20
5.0
52
.082
91.1
5529
822
246
3.34
9.0
95
.149
Totals for range
Jack
rabbits
per mi.
Cattle
38.9
Type
Acres
Semidesert
Miles
Jack
rabbits
TABLE 13.—COW-JACK RABBIT COUNTS, SANTA RITA RANGE.
*Mesa and foothill types could not be separated in this count.
JACK RABBITS
IN ARIZONA
559
Multiplying the number of cows, approximately 1,100, by 3.34 (cowjack rabbit ratio) we get 3,674, the total of jack rabbits. This checks
fairly well with the number determined by counts made previously (see
Table 12) during those times of day when rabbits were most numerous.
Many jack rabbits were doubtless missed on these counts, but it is perhaps safe to assume that we saw half of the rabbits. If this be correct,
the true number of jack rabbits on the 77 square miles of the Range
would be twice 3,674 or 7,348. W e conclude that the permanent population of jack rabbits on the Santa Rita Range probably does not exceed
10,000 and may not be over half that.
Segregating jack rabbits by species (see Table 14), we find a notable
difference in the distribution of Lepus alleni and L. californicus by vegetation types. There appear to be 2.8S L, alleni to each L. calif o? nicus
in the semidesert type, 5 alleni to each calif ornicus in the foothill type,
and 11.35 alleni to each calif ornicus in the mesa type.
Lepus alleni is apparently least abundant, on an acreage basis, in the
semidesert type (0.062 per acre) ; it is only slightly more abundant in
the foothill type (0.075 per a c r e ) ; but in the mesa type it is approximately three times as abundant (0.214 per acre) as in either of the
others.
W i t h Lepus calif ornicus the situation is different. This species seems
to decrease quite regularly from the semidesert type, where it is most
abundant (0.022 per a c r e ) , through the mesa type where it occurs at
the rate of 0.018 per acre, to the foothill type, where it is 0.015 per acre.
PELLET COUNTS
In captivity rabbits regularly defecate while they are feeding or very
soon after. Field observations indicate similar habits on the part of
hares in the wild. The utility of the pellet count depends in part on
this observed relationship between feeding and defecation. There is a
significant relationship between numbers of pellets and abundance of
jack rabbits on a given area. Though it %ives no information on absolute numbers, the pellet count is a reliable method of determining relative abundance.
The question has been raised, with reference to our experimental
plots, whether there is not an abnormal concentration of rabbits in the
cattle exclosures, where grass is sometimes more abundant than outside,
and into which rabbits may range freely. The most convenient way of
checking this point is the pellet count
JACK RABBITS IN ARIZONA
561
The pellets on 60 square feet were counted within the rodent-grazed
plot, or cattle exclosure, where concentration might be expected; and
the pellets on 120 square feet were enumerated in four places on the
open land outside the fences. The counts were taken with a circular
hoop inclosing 1 square foot of area. The hoop was placed on the
ground, the pellets counted, the hoop picked up and the observer walked
50 feet, placing the hoop again, just as it came. This method gave
counts from 1 square foot at 50-foot intervals along a line of 1500
feet. Results shown in Table 15 indicate no concentration of jack rabbits in the rodent-grazed plot, indeed, they show that jack rabbits do not
occur so commonly in that area as they do in the less well-grassed tract
outside. Later pellet counts, made during an unusually dry period,
show some concentration in the rodent-grazed plot.
A considerable number of pellet counts taken in a similar manner in
the different vegetation types of the Santa Rita Range shows that jack
rabbit pellets per unit (square foot) are considerably more abundant in
the mesa type (2.45) than in the foothill (0.75) or the semidesert
(1.85). Individual jack rabbits per unit (section) actually counted in
the mesa type (149) were also considerably more abundant than in
the foothill type (60) or in the semidesert type (54).
The number of jack rabbits actually counted in the mesa type was
about 2y2 times as great as in the foothill type, while the number of
jack rabbit pellets counted in the mesa type was about 3.3 times as great
as in the foothill type. The number of jack rabbits actually counted in
the semidesert type was slightly less than in the foothill type. Pellets
counted in the semidesert type, however, were considerably more than
twice as numerous as in the foothill type, showing a discrepancy between
data on numbers derived from counts of jack rabbits and those derived
from counts of pellets (Table 16).
TABLE 16.—PELLET COUNTS AND RELATIVE ABUNDANCE OF JACK
RABBITS BY VEGETATION TYPES ON SANTA RITA RANGE.
Type
Area
counted
square feot
Jack rabbit
pellets
Pellets per
square foot
Jack rabbits
counted
per section
Foothill
428
321
.75
60
Mesa
594
1454
2.45
149
Semidesert
569
1054
1-85
54
1591
2829
Totals
Average
1.777
JACK RABBITS
IN ARIZOXA
563
It appears that jack rabbits are less easily seen in the burrow eed of
the semidesert type than m the more open grass of the foothill type.
T h e pellet counts suggest also that rabbits are less easily seen in the
mesa type than in the foothill type, though the discrepancy is not so
great as it is between foothill and semidesert. /,. californkus which, it
will be remembered, occurs more commonly in semidesert than in any
other type, often escapes view by sneaking away in some shallow wash.
L. alleni, on the other hand, runs characteristically across the washes
and in the open. It is probable that californkus evades notice more often
than does alleni.
It is of interest that 2,829 jack rabbit pellets were found on 1,591
square feet of surface, counted at wide intervals over the Range, in all
the main vegetation types. Four hundred and eighteen pellets weighed
89 69 grams, or 0.21456 grams per pellet The pellets on a square-foot
average 0 3815 grams, and on an acre 36 61 pounds. For the 50,000
acres of the Range this amounts to 1,830,500 pounds, or 915 tons. This
is approximately 30 times the weight of the living jack rabbits on the
Range
GRASS AND JACK RABBIT ABUNDANCE
Contrary to our original opinion, detailed studies indicate that it is
not true that jack rabbits are most abundant where the grass is best
within their range. L. alleni reaches its maximum under conditions of
moderate grass growth, as on the mesa type. It is less abundant both
in the better-grassed foothill type and in the poorer-grassed semidesert
type. Even in the mesa type, alleni is apparently less abundant where
the stand of grass is excellent (Plate 12, A) than where the grass is of
poorer stand and more mixed with weeds (Plate 12, B). (See Table 17.)
L. californicus is more abundant in the poorly grassed semi-desert type
(Plate 12, C) than it is m either the better-grassed mesa type or in the
foothill type, where the best stand of grass in the region is to be found.
This observation has a very practical bearing. It indicates that the
stockman will make no mistake in conservative handling of his range;
that jack rabbits will not necessarily increase to consume the surplus
of the grass left by cattle; and that if a range is allowed to run down,
jack rabbits are likely to become more, rather than less, abundant, at
least up to a certain point.
The reasons for the above findings are not entirely clear. It is not
at all impossible, however, that the jack rabbit is more partial to some
of the weeds and herbs of the secondary successions that accompany
TECHNICAL BULLETIN No. 49
564
overgrazing, than to an exclusive diet of the climax grasses. (See p.
541). Also there are more mesquites (on the Santa Rita) on the overgrazed areas. There is a possibility, also, that like so many rodents,
the jack rabbits prefer open country with high visibility, to areas where
the grass prevents seeing far.
TABLE 17.—PELLET COUNTS, MESA TYPE, SANTA RITA RANGE,
ARIZONA, APRIL, 1932.
No of pellet
counts
Square feet
Total
Per square foot
In excellent grass ;*
Eriopoda Station (2B)
120
264
220
In poor grass ;f
Rodent Station (1A).
120
515
429
Location
No of rabbit pellets
* Good stand of Bouteloua rothrockn, burroweed scattered. Annual Bouteloua
and Atisiida scattered.
fMuch bare ground, burroweed abundant
Annual Bouteloua and A>tstida,
some Bouteloua roihrockii, mostly scattered.
ESTIMATED WEIGHT OF JACK RABBITS ON THE RANGE
As estimated by us, there are some 7,500 jack rabbits on the 50,000
acres of the Santa Rita Range. The weight of these animals is of
interest. According to our counts, 1,085 of the rabbits are L. calif ornicus. As the average californicus weighs 5.5 pounds, the total weight
of this species on the range is 5,967 pounds. On the same basis there
are 6,665 L. alleni on the range. This species weighs 8 pounds on the
average, the total weight for the Range being 53,320 pounds. The total
weight of jack rabbits is 59,287 pounds. The 1,100 cattle on the Range
at 750 pounds each would approximate 825,000 pounds in weight. Thus,
the jack rabbits, on a liberal estimate, weigh but 7.18 percent as much
as the cattle.
ECONOMIC STATUS
Jack rabbits may injuriously affect three great resources: farm crops,
range, and forest.
CROP DAMAGE
Where cultivated crops are grown in jack rabbit country serious damage frequently occurs. The injury may be increased by an unusual
abundance of the animals over a large territory, as has occurred repeat-
JACK RABBITS IX ARIZOXA
565
edly in California, Oregon, Washington, Idaho, and other states, but of
which we can find little evidence in southern Arizona. Serious damage
may also occur, however, as a consequence of local concentration resulting directly from drouth and shortage of succulent food outside
irrigated areas. Such concentrations have been unmistakable in southern Arizona in "bad" (drouth) years, where they occur mainly as nocturnal incursions from the surrounding "desert." Alfalfa, orchard and
ornamental trees, young cotton, and many minor crops are thus attacked.
In 1923 Taylor and County Agent C. B. Brown made a survey of jack
rabbit damage in the Marana district, Pima County, Arizona. Eightyeight acres of young cotton had been completely destroyed, with loss
estimated at $15,000. The damage was confined to farms adjacent to
brush land, and within one-half mile of such cover The same year a
Casa Grande, Arizona, farmer lost 20 out of 180 acres of cotton. A
rancher at Servoss, Cochise County, Arizona, during this same exceptionally dry season lost 14 acres of alfalfa through jack rabbits. After
summer rains had produced abundant food on the desert, ranchers reported no further trouble.
Similar losses occur all over the West, as indicated in reports by
Jewett (Oregon), Palmer (California), Couch (Washington), and Preble (Oregon). The last-named definitely refers to the dry condition of the
surrounding country as a cause of the jack rabbit raid on crops. Bailey
reported from Oregon that "In fields of young alfalfa and grain the
rabbits often take a large part of the crop or all of it unless fenced
out. . . . Tn a dry season, the loss from them is more serious than when
there is more rain and more vegetation/3
It seems clear that in cases of crop damage artificial control of rabbits must be exercised or adequate protection by fencing provided.
RANGE DAMAGE
A very large part of Arizona is devoted to grazing. Indeed, range
lands occupy about 88 percent of the area of the State, and comprise
some 64,000,000 acres. Similar proportions hold for much of the
western United States, where grazing is an important industry.
In southern Arizona, and doubtless in many other localities, always
excepting areas where the prairie dog is abundant and uncontrolled,
jack rabbits probably do more damage to range lands than any other
gnawing animals. It is a remarkable fact, however, that few jack rabbits are found on the extensive and well-grassed Empire Ranch country,
east of the Santa Rita Mountains, or the San Rafael Valley to the
south, along the international boundary, while on the beautiful ranges
566
TECHNICAL BULLETIN
No. 49
of the Altar Valley the animals are plentiful along the washes. These
areas, with or without jack rabbits, conservatively grazed by cattle,
seem to refute, so far as the jack rabbit is concerned, the sweeping state
ment quoted by Barnes (1926, p. 14) that "Not only have the ranges
been over-stocked but the prairie dog and the jack rabbit have also been
damaging the land until the best natural grass country in the United
States has been almost destroyed." Does not the jack rabbit get too
much blame for the results which come primarily from over-stocking ?
Nevertheless, figures already given, see pp. 516 to 521, and 523 to 525,
clearly indicate that jack rabbits destroy an appreciable amount of forage. As already stated (p. 527) there is no evidence that mesquite is
damaged by rabbits. On the contrary^ mesquite has apparently increased
substantially since 1900 on the Range and is probably a factor in crowding out the grass. The condition of vast areas in southern Texas, where
mesquite and prickly pear have nearly taken the country, may be a
warning for us. Mesquite and cholla are certainly increasing on many
of our heavily grazed areas.
When winter range is poor and the green bases of the grasses short
and difficult for cattle to graze, rabbits can still feed on them and thus
may further reduce the possibility of utilization by cattle. The damage
to grasses would doubtless be more serious than it is were it not for
the fact, confirmed by these studies, that jack rabbits at times of grass
shortage turn increasingly to mesquite and cactus.
We are not, however, in position to say that jack rabbits reduce the
carrying capacity of range lands in this region by 25 percent or any
other figure. Local conditions are so various, and the problem so complex, that any such statement would be misleading. Problems of jack
rabbit damage to range are local. Each community is a problem in
itself. It will do little good to eliminate jack rabbits, even where they
are superabundant, if an area is being" persistently overgrazed by livestock.
FOREST DAMAGE
A number of references to rabbit damage in the forest have been
made (see p. 511 et seq.). No reports have been received, however,
of this sort of injury in the Southwest.
VALUE OF JACK RABBITS
Inasmuch as the jack rabbit has been generally considered, if not a
pest, at least useless, it may prove surprising to see assembled the evidences of its positive value. Jack rabbits have proved to be valuable
JACK RABBITS
IN ARIZOXA
567
for their skins, for human food, as food for fur-bearers, and as a
safety factor for game and domestic livestock.
The largest item is that of returns from skins, which but a few years
ago could not be sold at any price. Sales in Washington State for the
winter of 1928-1929 were estimated by the Biological Survey at 4,000
white-tailed jack rabbit skins at $1.15 per pound, and 150,000 blacktailed jack rabbit skins at 75 cents per pound. In the United States, in
1929, 8,000,000 pelts were sold for about $2,000,000. In Australia, in
June, 1927, over 30,000,000 rabbit skins were marketed (Kinghorn, pp.
211-213, 1928), nearly £3,000,000 being the return during that month
for skins alone. While, as Kinghorn states, the various credits do not
compensate for rabbit damage done, surely there is nothing against
making a pest pay in cash as well as with its life for some of the injury
it does.
Various Indian tribes long ago discovered methods of making warm
sleeping robes from rabbit skins. Such robes are found in burials of
the ancient cliff and pueblo dwellers of the Southwest.
As food jack rabbits are not popular with the rural white population,
but they are in some demand among the poorer classes and foreign
elements of cities. Bailey in 1916 reported that Lepus c. wallawalla
had been shipped to Portland in large numbers at 10 cents each. Vorhies reports that in Salt Lake City (19104915) jack rabbits sold readily
at 25 cents per head, and that large kills of a thousand rabbits made on
winter holiday drives for charity were eagerly taken. In southern Arizona the poorer Mexican population consumes jack rabbits whenever
they can be obtained. A large agricultural project near Tucson some
years ago found its fields seriously damaged by jack rabbits. The management solved the problem by providing the Mexican laborers with
cheap .22 calibre rifles and ammunition at cost.
As a supplemental feed for hens, jack rabbit carcasses are valuable.
The meat diet added to other rations produces eggs at an accelerated
rate. While the American farmer may dislike to take the trouble to
shoot jack rabbits on his fields morning and evening for his poultry
this suggests itself to us as a feasible practice which would often pay
good profits. At the same time control would be exercised precisely
where and when most needed.
THE JACK RABBIT A SAFETY FACTOR
It seems clear that the existence of a fairly generous supply of jack
rabbits affords some protection to wild game and domestic animals by
diverting the attentions of coyotes and other carnivores.
568
TECHNICAL BULLETIN
No 49
Some years ago Preble (1908, p. 212) called attention to a similar
relation between rabbits, varying hares, and game in the AthabaskaMackenzie region. He said that many large game animals, and even
sledge dogs, were destroyed by wolves when rabbits were scarce.
A significant interrelation of similar kind was emphasized a few
years ago by Cabot (1912). In Labrador in the year 1905 mice of
various species reached a peak of abundance. Predatory creatures of
all sorts fed on the mice. Abundance of mice therefore tended to build
up the ptarmigan and the caribou through diverting the attention of
flesh-eaters from the game species. The next year the mice disappeared.
The consequent change in the wild life was remarkable. The wolves
attacked the caribou, and the predatory birds the ptarmigan, both game
species being much reduced. The mouse population affected all the
game, food, and fur species in the region.
Cabot also presents some significant information regarding the rabbit
in Labrador. He writes that the rabbit (varying hare), the caplin, a
fish of coastal waters, and the mouse exist mainly to feed their predatory
superiors, and possess an importance quite beyond their apparent insignificance. In years of rabbit scarcity in Labrador the Indians do not
hunt the districts where there are no lakes to provide a supply of fish.
In these years the lynx, the chief rabbit hunter of them all, is said not
to breed. The hardship of the rabbit's absence is felt also by the martens, by birds of prey, and by other hunting creatures. Thus it is that,
as Cabot says " . . . one may well touch his hat with respect when the
name of the Indians' 'Little White One* is mentioned."
Of course the values mentioned by Cabot are those of a primitive
northern country, where great and apparent fluctuations in animal population are the rule. While the case is far different in our own Southwest, there is no doubt in our minds that, in small or moderate numbers, the jack rabbit will be of neutral or even beneficial status on all
but cultivated lands.
A number of careful observers have noted increased coyote depredations following decrease in rabbit numbers. For example, a definite
statement to this effect by Benjamin Lawton, chief game guardian and
wolf bounty inspector for the Province of Alberta is quoted by Hewitt
(1921, pp. 199-200). Hewitt also points out (p. 211) how the numbers of rabbits affect the grouse. He explains that in its normal haunts
the goshawk preys on the rabbit and grouse. When rabbits are abundant the hawks increase in numbers and when the rabbits periodically
disappear the hawks attack the grouse in greater numbers.
Bailey says (1928, p. 61), in the Carlsbad region of New Mexico,
JA CK RABBITS JX ARIZO XA
569
"Out over the dry flats and ridges only an occasional rabbit was seen,
and their total numbers would probably not average more than three
to a square mile of the valley country. In this scattering and about
normal abundance they are of little economic importance and may prove
an asset rather than a liability, for they feed the coyotes, eagles, hawks,
and owls and thus prevent more serious depredations on livestock and
game/'
Leopold (1931, p. 96) refers to the known importance of the snowshoe rabbit in diverting predators from more valuable game.
In 1930 a stockman on the Lemhi National Forest told S. B. Locke
that there were many more rabbits in the old days when coyotes were
thick, than now. It was his opinion that the present scarcity of rabbits
and sage grouse caused the coyote to live principally on sheep, so that
even with fewer coyotes, the damage was proportionally greater. On
the contrary, Foster is of the opinion that the removal of jack rabbits
in the Congress Junction area, Arizona, has had no influence whatever
in turning the attention of coyotes to sheep. He believes that the extent to which coyotes control rabbits or rodents is in direct proportion
to the amount of domestic livestock. When sheep are available, coyotes
will not eat many rabbits since it is much easier, he points out, for the
coyote to kill a young lamb than to catch a jack rabbit.
Nevertheless, we feel that there is much evidence to indicate that a
normal population of rabbits and rodents which form the food for a
variety of flesh-eating birds and mammals is an important safety factor
for quail, fawns, sheep, and calves.
CONTROL
RABBITS IN AUSTRALIA
An interesting and significant picture of what might happen in this
country in the absence of natural checks on jack rabbits is afforded by
the story of the introduction and increase of rabbits in Australia. Since
this story for the most part is unfamiliar to American farmers and
stockmen, we have outlined it here.
The introduced rabbit which is such a pest in Australia is not a
hare, but the rabbit from the Continent of Europe, Oryctolagus cuniculus (Miller, 1912, p. 485) secondarily introduced into England, South
Africa, and elsewhere.
The exact date of the introduction of the rabbit into Australia is
unknown. Kinghorn (1928, pp. 211-213) refers to the establishment
570
TECHNICAL BULLETIN
No. 49
and increase of rabbits introduced by Governor King as early as 1791;
while Matthams (1921, p. 18) refers to an importation made by Thomas
Austin of Barwon Park in 18S9 as the first to become acclimatized on
the mainland. Suffice it that the climate and soil of Australia suited the
rabbits perfectly, and their natural enemies were too few and too weak
to keep their numbers within reasonable bounds.
While at first the rabbits increased and spread very slowly, being the
prey of eagles, hawks, and native cats (presumably Dasyurus), at
length they secured a firm footing and commenced to expand in a terrifying manner. In spite of all attempts at suppression, the rabbits
steadily overran the country until, at present, almost the whole of the
Continent is well within their grip.
By 1921 (Matthams) the total amount spent by the Australian Government approached £200,000 per year in addition to large sums spent
by landholders and to the colossal losses suffered through the consumption and destruction of pasture and produce.
As the rabbit numbers increased the people were not idle, and vigorous
attempts were made to bring the pest under control. At different times
there were employed as major projects introduction of natural enemies,
disease, and various methods of eradication, including poisoning, digging out of dens, destruction of vegetation, and a bounty system of
killing.
The Australian predators proving impotent in the face of the rising
menace, many attempts were made to bring in the natural enemies of
rabbits from Europe. At different times stoats, weasels, ferrets, and
foxes were imported. None of these species was effective.
Stoats and weasels are well known to be bloodthirsty animals, killing
more than they require to satisfy their wants. They proved serviceable,
explains Matthams, especially in rocky and forest country, although they
did not keep the rabbits suppressed to a satisfactory extent. Ferrets
were extensively bred and released by thousands on Crown lands, espeially in New Zealand. While they kept certain areas fairly free from
rabbits, they were suspected of more driving away of rabbits than
actual destruction. In the seventies foxes were introduced into Victoria by the Melbourne Hunt Club for sporting purposes. By 1921 thousands were roaming about Australia. Their principal food is rabbits.
In all these cases of introduced predators it is difficult to prevent
their depredations on valuable life, including domestic poultry, lambs,
native wild life, and introduced game. When rabbits became scarce the
stoats, weasels, and ferrets turned to poultry yards and ground-nesting birds. In New Zealand they exterminated the introduced game
JACK RABBITS
IX ARIZONA
571
where it was once plentiful. The fox, likewise, readily turned to lambs,
poultry and bird life. Apparently all these foreign predators have
themselves become serious pests.
The bounty or "bonus" system was apparently given a thorough
trial and it is reported that in 1887 bounties were paid on 27,000,000
scalps in New South Wales alone. Between 1883 and 1888 (when the
bonus system was discontinued) expenditures for bounties aggregated
£917,000.
None of these various means was found superior in actual killing
of rabbits to the laborious digging out of burrows, use of poison
(strychnine, phosphorus,* arsenic, and poisonous gases) and elimination of cover practiced from the first.
In something like desperation the Government of New South Wales
offered a reward of £25,000 (August 3 1 , 1888) to anyone who could
demonstrate an effective means of exterminating rabbits (Matthams,
1921, p . 121). Although a good deal of activity was stimulated by this
offer and a number of diseases introduced in a limited way they were
not effective. There was always the chance, too, that the disease would
spread to desirable wild life.
BIOLOGICAL
CONTROL
Principles of biological control as applying to prey-predator relations among vertebrates have received far less attention from research
workers and wild life administrators than their importance deserves.
I n attempting to formulate our own opinions we have been much helped
by the analogy between these prey-predator relations among the vertebrates and bird-insect relations. Certain papers in the latter field by
McAtee (1920, 1926, 1927, 1928, 1931) have been particularly illuminating. W e propose the following tentative principles, largely paraphrased
from McAtee, which we believe to be applicable.
1. Predators almost invariably specialize on the most abundant or
most easily accessible food supply.
This is a commonplace of field experience. When rabbits, rodents,
or insects are superabundant, they will be given special attention by
flesh-eaters.
T o a degree, at least, natural checks act automatically
in a manner similar to the governor on a steam engine.
2. Predators must be judged on their average economic tendencies
It is of interest that phosphorus is or has been used m Australia, apparently
extensively, in spite of complaints of damage to valuable wild life. This poison
is so dangerous that in the United States its use is rigorously avoided if not
prohibited.
572
TECHNICAL BULLETIN
No. 49
rather than on local activities and seasonal or otherwise exceptional behavior.
We are beginning to realize the error of appraising our "predatory"
mammals on the basis of the most serious depredations of individual
offenders. Snap judgments as to the true status of flesh-eating or other
specks either of birds or mammals, are almost sure to be wrong.
3. Control measures should not be applied to a whole species of predator on the basis of damage done locally. The proper remedy for local
and sporadic depredations by flesh-eaters is local and temporary control.
The Biological Survey has repeatedly emphasized the need for confining control activities to particular limited localities. The necessity
for this is increasingly realized, both from the standpoint of the biology
of the situation, and of the economical use of State and Federal funds.
4. Rabbit, rodent, and insect control, aside from that applied by
man, is due to a combination of all inimical factors — unfavorable climate, predators, parasites, diseases, and innate defects in the herbivores
themselves — in other words, the whole environmental complex.
5. Probably the most useful function of predators is in their constant cutting down of the numbers of herbivores and insects in general,
and not in their more spectacular services in the presence of rabbit,
rodent, or insect plagues.
The value of biological controls in preventing animal plagues by nipping them in the bud is one that is frequently overlooked. A predatory animal may be an effective check when the numbers of its prey are
small, whereas it may be of negligible influence if the food species breaks
out of bounds and attains to plague status. In this connection see
Hall (1927, p. 202).
6. Predators, where present in normal numbers, are a reasonably
mobile force against rabbits, rodents, and insects and sometimes gather
at the scene of an outbreak.
7. Predators are only one of the natural forces regulating the numbers of rabbits, rodents, and insects: it takes all the natural forces together to do the job.
Under the artificial conditions man has created it will sometimes be
necessary for him to supplement the activities of all these natural forces
and combat the rabbits, rodents, and insects directly to secure the degree of control necessary to commercial success.
8. Under normal conditions the natural enemies of rabbits, rodents,
game, and insects live on population surpluses; the "interest" only is
taken, the "capital" being left intact.
IA CK RABBITS IX ARIZO \\ 1
573
9. Good economic tendencies are as satisfactory as any grounds for
advocating the protection of predators.
In a real sense Huxley (in Elton, 1927, p. xiv) is right when he sa}s
the existence of enemies is a biological necessity to a species, as it prevents disastrous over population. So long as a normal number of natural checks is present, we probably need not be concerned, under ordinary conditions, about the breaking out of rabbit plagues. But it is a
forlorn hope to depend on the flesh-eaters to "control" rabbits or rodents
in the sense of eliminating all losses. In all probability control in this
sense would seldom or never result from the natural enemies of a "pest"
species. For the welfare of the predators is dependent on a continuing
supply of their food. Nevertheless, the services of the flesh-eaters in
preventing the undue increase of a "pest" species may be appreciable,
and fully warrant, in some localities, retaining the carnivores for their
services in this regard.
Changes in conditions following upon occupation by man are responsible for modified and often problematic status. Ligon (1927, p. 49)
writes that "Formerly when wild life had few other enemies, predatory
animals exerted little influence on its abundance. In fact, predatory
animals under primitive conditions were decidedly beneficial in preventing
superabundance and in eliminating the weaklings and unfit. Furthermore, they were potent factors in the process of distribution. But today
we have an entirely different ratio of hunters to hunted. Then, too,
game and game ranges have been greatly reduced, and predatory animals,
naturally, harbor where the game finds protection from man. Compared with their prey, in the limited cover where the remaining game
ranges, coyotes, because of more recent adaptations, are more numerous. Wildcats, which are serious enemies of game, are also numerous
in most game covers." This discussion well illustrates the present-day
point of view of the control man, the sportsman, and the livestock man.
There is little doubt that, as pointed out by Spencer in a letter to
the writers, disturbance of vegetation through overgrazing, deforestation, farming or reclamation, is more far-reaching in its effects on rodent
numbers than are the flesh-eaters. This observation accords also with
that of Leopold, who has found that provision of cover and other environmental conditions is much more important to the conservation and
increase of game than control of flesh-eaters.
Lantz (1917a, p. 17) has emphasized the need for better protection of
coyotes, foxes, wildcats, badgers, skunks, minks, hawks, owls, eagles,
and snakes, as enemies of rodent pests of the farm. He asserts that
much of the damage now done by rodents is due to the unceasing war-
574
TECHNICAL BULLETIN No. 49
fare waged against carnivorous animals, the fact that they destroy far
more noxious rodents than they do useful animals being forgotten. He
has pointed out, also (1918, p. 22) that many of our fur animals are
an asset to the country, equal in value to our game, and that their
destruction has often proved of no real help to game conservation.
ORGANISMS
OF DECAY
BACTERIA
(f
/
dfInsectivorous) b
\
^)
BIRDS (Raptores) /
BIRDS
MAMMALS \
MAMMALS (Predators)
HawKs
y Thrashers
Grasshopper Mice V
Coyotes
°S> INSECTS C a c " e n 5 Ground Sorrels S h £ K E S
Bobcats
(rVedac.ous) f
/>
LIZARDS
GAME BIRDS
6ambel Qua
Scaled Qua
Mourning Dov
BROWSE SPECIES
Mesouite
Cat's Claw
Cactus
INSECTS
Grasshoppers
Beetles
Ants
RABBITS
Antelope and
California
Jack-rabbits
GRASSES
Grama Srass
Needle Grass
Sporobolus
HERBS
Eschscholtzia
Porfulaca
Plants go
to S
CC
C
Squirrels
Mice
Wood Rails
TREES
Hackberry
Oaks and
Others
2
ATMOSPHERE
PHYSICAL—CHEMICAL— BlOTIC
""PHYSICAL- CHEMICAL— BIOTlC
Fig. 5.—Tentative diagram of bio-physical complex on the Santa Rita Range.
JACK RABBITS IN ARIZO XA
575
We sometimes hear the argument that it is essential to get rid of the
coyote so that the game can become more abundant. Often equally
emphatic arguments are heard that the coyote has no appreciable effect
on rabbits; that killing the coyote will not result in appreciable rabbit
increase. We feel it would be thoroughly inconsistent to urge that
the removal of coyotes permits the appreciable increase of game, but
not the appreciable increase of jack rabbits and other rodents, even if
the coyote fed equally on game and rodents: but as a matter of fact,
rodents, and especially rabbits, figure to a much greater extent in coyote
diet than does game.
To our mind the evidence shows that where anything like normal conditions prevail, it is best not to try to exterminate either the jack rabbits or their predatory enemies. The policy of the Biological Survey and
of some of the states concerned is in full accord with this conclusion.
The presence of jack rabbits may appreciably relieve predatory pressure
on desirable game and livestock. The presence of flesh-eating mammals
and birds is a factor of unknown importance in preventing plagues of
rabbits, rodents, and insects (Fig. 5).
T H E BALANCE O F N A T U R E
Under original conditions the forces of nature, predators, parasites,
prey, all the complicated physical, chemical, and biotic factors, were in
equilibrium of a sort. Sometimes this wTas violently fluctuating, but
nevertheless following an inexorable law of compensation. There is no
question that in the realm of bio-ecology, as in physics and chemistry,
for every action there is an invariable and inevitable and absolutely
equal reaction. This balance of cause and effect must have held as long
as the universe has been operating on uniformitarian as distinguished
from catastrophic principles.
Much skepticism has been expressed, of late, of the reality of the
balance of nature. We are of the opinion, however, that the phrase is
pertinent and accurate. Nor can man affect the situation at all, in the
sense of eliminating the balance. He has blithely and necessarily upset
the original balance, and he can further disturb the present balance. In
any case, a new balance of forces must ensue. He may abstract a
weight here or put another there, but he can never destroy the balance
any more than he can prevent the conservation of energy. The new
balance may be more to his liking, or it may be extremely harmful to
him. It is man's job to understand the balance well enough to be sure,
when he changes it, that the new arrangement will be to his advantage.
576
TECHNICAL BULLETIN
No. 49
The fact that man as yet understands very little of the natural world
is an excellent argument that he should be cautious in upsetting nature's
arrangements.
Marsh has well said (1898, p. 143) "As often as we destroy the balance by deranging the original proportions between different orders of
spontaneous life, the law of self-preservation requires us to restore the
equilibrium, by either directly returning the weight abstracted from one
scale or removing a corresponding quantity from the other. In other
words, destruction must be either repaired by reproduction or compensated by new destruction in an opposite quarter."
This means that if we reduce the natural predatory enemies of jack
rabbits for whatever reason, we shall probably have to plan for an increase in rabbits. Destruction necessitates further destruction. As
repeatedly asserted by the Biological Survey and others conversant with
the situation, extermination is not a justifiable objective. To paraphrase Romell slightly (1930, p. 842) we may say "Everything indicates that in the future the administration of natural resources will have
to rely still more than now on natural equilibria." The best control
program is that which interferes least with the orderly relationship of
natural species, but which at the same time, helps to assure success to the
agriculture, range management, and forestry on which man depends for
his own existence.
DIRECT METHODS
It has long been recognized that direct control of the jack rabbit is
one of the most difficult of all the control problems which trouble the
farmers of the Southwest and the Federal and State agencies which attempt to help them. One reason for this is that in the mild climate of
the Southwest rabbits do not concentrate in winter as they do in the
more extreme northern climates, and so are much less easily poisoned.
Federal and State agencies have been working on these problems and
have devised some good methods. Control must of course be adapted
to local conditions. The isolated farm or small community surrounded
by much wild land may be able to use poison alfalfa, but in the long
run will probably find it cheaper to fence against the jack rabbit, or as
previously suggested, to shoot the animals day by day and use the carcasses for poultry feed. Rabbits killed in excess of present need may
be preserved in our arid climate by immediately skinning, gutting, and
hanging them Tip to dry.
Gilchrist has worked out a careful comparison of the relative costs
of shooting with a .22 calibre rifle and of poisoning, as follows:
JACK RABBITS IK ARIZONA
577
Shooting
Labor of 1 man 8 days at $2.50 per day
1,000 .22-calibre rifle cartridges at $5.00 per thousand
13 gallons gasoline at 25 cents per gallon used in car while
travelling 191 miles shooting jack rabbits
1 gallon lubricating oil at 30 cents per gallon
$20.00
5.00
Total cost of shooting 859 jack rabbits
Cost per rabbit shot
$28.55
0.0332
3.25
30
Poisoning
Labor of 1 man 4 days removing stock and prebaiting
$10.00
Labor of 1 man 4 days placing poison
10.00
173/1 ounces strychnine at 57 cents per ounce
10.12
355 pounds of fresh alfalfa for pre-bait at 1 cent per pound
3.55
355 pounds of fresh alfalfa for poison bait at 1 cent per pound.. 3.55
Total cost of poisoning 962 jack rabbits
Cost per jack rabbit poisoned
$37.22
0.0387
These demonstrations were on a comparable scale of size, and were
in the same general region, near Willcox, Arizona. The cost of poisoning was more than J4 cent higher per rabbit than the cost of shooting,
or 16}4 percent more expensive. This cost differential may result from
failure to find all poisoned rabbits.
In connection with this excellent showing for the shooting method
it may be pointed out that the use of poison has certain disadvantages.
Not only may valuable livestock be accidentally poisoned, but harmless
or beneficial wild life may occasionally be destroyed. Poisoning of
pest species of animals has been advocated and practiced to a greatly
increased degree in recent years, but the poisons and poison baits are
not ordinarily specific and are very difficult to handle in a manner
above criticism. Poison should be used only under supervision of State
or Federal officers. Otherwise it may be expected that its abuse will
eventually bring about the passage of strict legislation against the use
of poison.
Since most cultivated fields are already fenced against livestock, the
expense of adding the necessary netting to make a rabbit-proof fence
is not great. An effective, though not very permanent, job can be done
with the cheapest material, common poultry net. Where the first cost
can be met, a more durable net will pay in the long run. This fence
must be tight to the ground, since the rabbits will crawl or even burrow
578
TECHNICAL BULLETIN
No. 49
under rather than go over. Two-inch mesh poultry net, 2 feet in
height, is ordinarily sufficient to turn rabbits. Occasional inspection
for entrance burrows will be necessary.
Rabbit drives, being spectacular (and, where shooting is a part of the
drive plan, appealing to man's sporting or killing instinct) sometimes
result in the destruction of impressive numbers of jack rabbits. Since
this method is most successful where and when very dense rabbit populations occur, and since extreme over-population of jack rabbits is relatively rare in Arizona, it is not much advocated here. If it were not
for the picnic and sports feature it would probably seldom be resorted to,
for if all the man power used in a drive were paid for at day-labor
wages, and the ammunition and gasoline used were charged against
the project, driving would prove to be an expensive method of control.
We regret that it has been impossible for us to hit upon any readily
applied formula which would tell just when control should be applied.
We have wrestled long with this problem, but have been forced to conclude that information regarding the economics of industry and of wild
life is not sufficient to permit of any simple statement.
As pointed out to the writers by Spencer, the time to determine optimum numbers of range-feeding rodents and rabbits is during the worst
years, when animal damage is greatest. Just as stock should be regulated on a basis of the numbers a range can carry in the driest years,
so attempts to limit the native vegetation feeders may well be guided in
the same way.
If a stockman or rancher has a rabbit problem, he should examine
the situation from the point of view, not alone of the damage done by
the rabbits, but also the possible benefits. Often there will be no question whatever regarding the need for control. State and Federal officials, including county agricultural agents and Federal leaders in rodent
and predatory mammal control, can be of great assistance and should
be consulted whenever damage becomes serious.
Where the problem is not so simple, and there is a question whether
jack rabbits are abundant enough and doing damage enough to warrant
control, the benefit should in all cases be given the existing condition.
A FUNDAMENTAL PRINCIPLE
In former days protection, with little reference to long-time results,
was the magical word in conservation of assumed valuable game. In
the same way extermination was the objective for control of alleged
pest species.
The more scientific management programs of the present day require
a readjustment of former aims. Protection of deer may be extremely
JACK RABBITS IX ARIZOXA
579
harmful if a surplus population grows up and overconsumes the available feed. Extermination of alleged pests is so often attended with costs
and difficulties that it must be abandoned as an aim of control.
The modern objective of game and wild life management is a normal population of wild animals. Judicious interference by man will
often be necessary to maintain optimum numbers. The question of
what is the optimum number of a particular species will have to be settled in each locality on the basis of its actual and potential values, the
damage it may do, and its often complex relationships, including the
interest of man in that particular place. This is wild life management.
SUMMARY
1. More and larger areas under natural conditions are needed for
the study of range problems.
2. Jack rabbits (hares) are readily separable from all other rabbits
by structural characters and habits. The antelope jack rabbit, L^pus
alleni, is readily distinguishable by its long white-edged ears and white
sides from the gray-sided jack rabbits, Lepus californicus ssp., which
have black-tipped ears and gray sides. L. alleni averages 8 pounds in
weight and L. c, ereinicus 5.5 pounds.
3. There are no apparent secondary sexual characters in the jack
rabbits.
4. Jack rabbits are admirably adapted structurally and also in behavior for successful life in an arid environment.
5. Lepus alleni is chiefly Mexican in distribution, occurring within
the United States in only a small part of southern Arizona. It inhabits somewhat open country chiefly below 4,500 feet altitude.
6. The Lepus calif ornicus group of jack rabbits occurs over practically the whole of the western United States, from the upper Arid
Tropical to the Transition Zone.
7. Lepus alleni shows some tendency to gregariousness, but in L.
californicus there is little or no such tendency. There is no evidence
of hybridization between the two species.
8. Daily movements of jack rabbits depend on food and shelter relations. Seasonal movements of relatively limited extent may take place,
usually in accordance with available food.
9. The rump-flash is a spectacular feature of the antelope jack rabbit.
580
TBCHMCAl BULLETIN No. 49
10. The senses of hearing and smell in the jack rabbit are particularly keen. Touch also, is probably sensitive. Sight is apparently less
useful than the others.
11.
The normal life span of jack rabbits is unknown.
12. The sex ratio is nearly balanced.
13. The breeding season of jack rabbits in southern Arizona is
long, extending from January to September.
14. Lepus californtcus produces more young per litter, average 2.24
(1-6), than L. alleni, average 1.93 (1-5). The litter averages vary by
months, showing a correlation with average monthly precipitation. Probably three or four litters are produced each season.
15. Jack rabbits probably scatter their young at or soon after birth,
though occasional nests have been authentically recorded. The young
are fully furred and active at birth.
16. Rabbit pressure may exercise a profound effect on plant associations. Man's disturbance of original conditions accentuates this
situation, and is frequently the cause of difficulties.
17. Calculations indicate that it takes IS Lepus alleni to eat as much
valuable forage as one sheep, or 74 as much as one cow; and twice as
many L. californtcus as L. alleni to consume the same amounts.
18. In our experimental plots on the Santa Rita Range jack rabbits
and rodents are apparently mainly responsible for holding the vegetation in a preclimax condition, preventing attainment of the climax grass
stage.
19. Stomach analyses available indicate that 36 percent of the food
of Lepus alleni is mesquite, and 45 percent grass; and that L. californicus consumes 56 percent of mesquite and only 24 percent of grass. On
these analyses it appears that grass and mesquite together constitute 80
percent of all food of both species. Unfortunately stomach analyses do
not give an adequate idea of weeds consumed. It is probable these figures by themselves would lead one to seriously underestimate the rabbit's actual liking for and consumption of weeds.
20. The evident fondness of rabbits for grass when available probably favors the encroachment on grass ranges of mesquite, cholla cactus, weeds, and other species.
21. It is estimated that jack rabbits consume less than 3 percent of
the potential production of grass on the Santa Rita Range.
JACK RABBITS
22.
IX ARI70XA
581
Jack rabbits are chiefly crepuscular and nocturnal.
23. Flesh-eaters, as the coyote, bobcat, and numerous other mammals, and a wide variety of hawks and owls, feed quite regularly on
jack rabbit and under normal conditions help to prevent over-population.
24. Jack rabbits are commonly infested with parasites, of which
Cuterebra larvae (warbles), ticks, and tapeworm cysts are most common. Fleas are fairly abundant. Tularemia, to which humans are also
susceptible, is the most important germ disease of rabbits, so far as
known. There is little evidence that any of these materially affect the
numbers of jack rabbits in southern Arizona.
25. The jack rabbit population in southern Arizona does not
extremes of variation. Fluctuations in numbers are more marked in
regions of greater temperature extremes, but maxima or minima occur
at different times in different localities.
26. Several methods of enumerating jack rabbits were tested and
checked against each other. The number of these animals on the 50,000
acres of the Santa Rita Range is probably between 5,000 and 10,000.
The jack rabbits are estimated to weigh only 7 percent as much as
the cattle on the Range.
27. Pellet-count methods were developed as a means of checking
on the relative abundance of jack rabbits on different areas.
28. Jack rabbits tend to be more abundant in open weedy areas
than in the best grass areas.
29. Jack rabbit effects, even if neutral at other times, may be important during the driest season of the year; jack rabbit pressure on
vegetation during the driest season of the driest year of a cycle is
likely to produce results more far-reaching than in any other year or
combination of years. Numbers should be regulated with this in mind.
30. Jack rabbits are of value for skins, as food for man and carnivores, and as a safety factor for game and livestock.
31. The experience of Australia should serve as a warning of what
might happen if the natural predator checks on rabbit increase were
completely removed. The best control program is one which interferes
least with the orderly relationships of natural species, but which, at the
same time, helps to assure success of the agriculture, range management, and forestry on which man depends for his own existence. Natural equilibria must be increasingly relied upon in administration of
natural resources.
582
TECHNICAL BULLETIN
No. 49
32. Consumption of grass by jack rabbits varies inversely with consumption of mesqmte and cactus. Conservative handling of grazing
ranges, including stocking for the worst years rather than the best or
even the average years, and retention of a normal population of flesheaters, may ordinarily be counted on to obviate serious rabbit injury.
Under conditions of overgrazing and of misapplied control of predators, there is almost sure to be a jack rabbit and rodent problem.
33. Rabbit drives in Arizona are not of great value for direct control. Poisoning and careful work under certain conditions with a 22
calibre rifle are reasonably effective, with the cost and other advantages in favor of shooting. For crop protection rabbit-proof fence is
best and cheapest.
34. In small or moderate numbers the jack rabbit may be of neutral
or even beneficial status on all but cultivated lands.
JACK RABBITS IK ARIZOXA
583
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